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METABOLISM AND NUTRITION |
* Department of Poultry Science, University of Arkansas, Fayetteville 72701; and Adisseo Inc., Alpharetta, GA
1 Corresponding author: jemmert{at}uark.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Key Words: broiler • methionine • homocysteine • remethylation
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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), is formed as part of normal Met metabolism and may undergo irreversible transsulfuration to Cys or remethylation to Met by folate–vitamin B12-dependent Met synthase (MS) or betaine (BET)–HCY methyltransferase (BHMT). The methyl group provided by BHMT is derived from BET, a product of choline (CHOL) oxidation. Differences in expression of enzyme activity have been noted in various species; MS is widely expressed in avian and mammalian tissues (Mudd et al., 1965; Finkelstein et al., 1971; Stipanuk, 2004), whereas BHMT has been detected primarily in the liver, with lesser activity levels occurring in the kidney (Mudd et al., 1970; Finkelstein et al., 1971; Finkelstein and Martin, 1984; Xue and Snoswell, 1985; Cao et al., 1995; Emmert et al., 1996, 1998). Thus, liver tissue contains substantial activities of both HCY remethylation enzymes.
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Because Met is the first-limiting amino acid in commercial poultry diets, there is a very large market for Met supplements, the most important of which are DL-Met (DLM) and 2-hydroxy-4-(methylthio) butanoic acid (HMB), a synthetic analogue of Met. Efficacy of HMB as a source of Met, particularly for young broilers, is still being debated. Efficacy estimates have ranged from 48 to 125% (Waldroup et al., 1981; Boebel and Baker, 1982; Muramatsu et al., 1984; Garlich, 1985; Esteve-Garcia and Llauradó, 1997; Lemme et al., 2002; Vazquez-Anon et al., 2003), and, although trial design has undoubtedly affected the results and interpretation of HMB efficacy studies, experimental diets have also varied greatly, particularly concerning dietary levels of Cys, CHOL, and BET, which are also known to affect hepatic SAA metabolism.
The objective of this research was to use a newly developed stable isotope technique (Pillai et al., 2006) to assess the effect of Met source and dietary SAA, CHOL, and BET levels on hepatic HCY remethylation. In addition, the effect of surfeit dietary CHOL and BET on HMB efficacy was assessed.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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In Experiment 1, a corn–peanut meal basal diet (Table 1) deficient in Met and Cys (and containing supplemental CHOL) was used. Dietary treatments (Table 1) were designed to contain graded levels of DLM or HMB (0, 0.04, or 0.08%; HMB as sold contains 88% HMB, and, therefore, an adjustment was made so that an equal mass of HMB and DLM was fed) fed alone or with isomethyl surfeit levels of CHOL (0.25%) or BET (0.28%). Actual DLM additions (from diet analysis) were 0.03 and 0.11%. In this experiment, a mixing error occurred, and all HMB treatments contained 0.04% HMB (Table 1); therefore, there were only 12 dietary treatments, and HMB treatments were replicated in 10 pens.
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) deficient only in Met (and containing supplemental CHOL) was used. Dietary treatments (Table 1) were again designed to contain graded levels of DLM or HMB (0, 0.04, or 0.08%; with HMB reflecting adjustment for 88% purity) fed alone or with isomethyl surfeit levels of CHOL (0.25%) or BET (0.28%). Actual DLM additions (from diet analysis) were 0.03 and 0.09%, and actual HMB additions (from diet analysis) were 0.04 and 0.10%. Therefore, Experiment 2 contained 15 dietary treatments. Methods for assessing HCY remethylation were described in detail by Pillai et al. (2006) and were based on an in vitro stable isotope technique similar to that used by Storch et al. (1988, 1991) and van Guldener et al. (1999). Frozen liver tissue was suspended in a buffer, homogenized, and centrifuged. The resulting supernatant was subjected to incubation with HCY (Aldrich Chemical Co. Inc., Milwaukee, WI) and a stable isotope of BET (D11 BET, Cambridge Isotope Laboratories Inc., Andover, MA) for 0 or 10 min, followed by HPLC mass spectrometry analysis for the quantification of Met isotopomers. Standardized peak area values were used to arrive at conclusions about remethylation of HCY. In this reaction system, Met formed through the MS pathway (native Met) has a normal molecular weight, whereas Met that formed through BHMT has a higher molecular weight; thus, data from the HPLC mass spectrometry analysis was useful in calculating the following parameters:
Statistical Analysis
Pen means were considered the experimental unit, and data were subjected to ANOVA (SAS Institute, 2004) as a completely randomized design; treatment means were separated using Duncan’s multiple-range test. Pre-planned single df contrasts were used to test overall effects of Met, HMB, CHOL, and BET (when appropriate). The amount of supplemental DLM and HMB chosen was that expected to result in weight gain in the linear portion of the growth curve. In Experiment 2, linear regression equations were calculated (SAS Institute, 2004), with weight gain per chick (g) as the dependent variable and consumption (mg) of supplemental DLM or HMB as the independent variable. After establishing that y-intercepts were not different (P > 0.05), the slope-ratio technique (Sasse and Baker, 1973; Boebel and Baker, 1982; Rostagno and Barbosa, 1995) was used to calculate the relative efficacy of HMB as a precursor of Met. A multiple linear regression equation was calculated (SAS Institute, 2004) that was composed of 2 straight lines with regression coefficients representing grams of gain per milligram of digestible Met intake from DLM or HMB. Potential differences between the sources were determined by a comparison of regression coefficients using a t-test (SAS Institute, 2004).
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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. In birds fed diets with and without surfeit CHOL or BET, weight gain increased linearly (P < 0.05), and there was a significant increase (P < 0.05) in feed intake and feed efficiency with increasing DLM addition. Single df contrasts indicated a significant (P < 0.05) increase in weight gain in birds fed surfeit CHOL or BET, with CHOL providing the greater (P < 0.05) response. Birds fed surfeit CHOL also had increased (P < 0.05) feed intake compared with birds fed diets containing no addition or BET.
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. In birds fed diets with or without surfeit CHOL or BET, addition of graded levels of both DLM and HMB resulted in linear (P < 0.05) increases in weight gain, feed intake, and feed efficiency. Overall, the growth response of birds fed the basal diet in this experiment was lower compared with the first experiment, which may be attributed to a basal diet that contained a lower level of digestible Met (Table 1), as well as differences in chick quality. Again, birds fed surfeit CHOL or BET exhibited a growth response (P < 0.05) when fed the most deficient level of Met (basal level), and there was a significant overall increase (P < 0.05) in feed efficiency in birds fed diets with surfeit CHOL or BET addition. It is interesting to note that, in Experiment 2, the response to supplemental CHOL or BET at the basal level was due to a feed intake and feed efficiency response, whereas in Experiment 1, the response was entirely due to increased feed intake.
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). Although the main effect of CHOL and BET addition on weight gain in Experiment 1 was significant, closer examination of the data indicates that it was the response of birds fed diets containing the first level of DLM or HMB that was largely responsible for the overall significance. Similarly, although there were significant overall responses to surfeit CHOL or BET in Experiment 2, these responses were virtually entirely due to significant responses to CHOL and BET at a single level of Met (basal diet). We previously reported similar responses (Pillai et al., 2006) in birds fed diets deficient in Met and Cys; weight gain increased in response to surfeit CHOL or BET at levels of Met supplementation similar to those used in Experiment 1 of the present study. Further, these observations are similar to those of Lowry et al. (1987) and Emmert et al. (1996), who noted a small increase in weight gain and feed efficiency of chicks fed a marginally Met-deficient diet when dietary CHOL was added. However, a commonality among these reports is that the weight-gain response to surfeit CHOL or BET in diets deficient in SAA was not of the same magnitude as the response to DLM. Other authors have noted a response to supplemental CHOL or BET in diets marginally deficient in Met, so that a portion of the Met requirement appeared to be spared (Quillin et al., 1961; Pesti et al., 1980; Virtanen and Rumsey, 1996). However, attempts to replace too great a portion of the Met requirement with BET have been unsuccessful (Rostagno and Pack, 1996; Schutte et al., 1997; Esteve-Garcia and Mack, 2000). In the current experiments, all treatments were designed to be deficient in Met; it is possible that the degree of Met deficiency precluded a response to supplemental CHOL and BET at each level of supplemental Met.
A pattern seems to be emerging in which a growth response to surfeit CHOL or BET (in birds fed diets already containing supplemental CHOL) occurs in birds fed diets either substantially deficient or slightly marginal in Met, but the inconsistent and somewhat unpredictable manner in which broilers fed SAA-deficient diets respond to surfeit CHOL or BET indicates that caution should be used when trying to replace a portion of the dietary Met requirement with either CHOL or BET. This thought was shared by Simon (1999), who suggested that attempts to increase substrate levels for BET- and folate-dependent HCY remethylation with the intent of generating Met is of limited application, even in young chickens.
Results from the stable isotope studies are shown in Tables 2 and 3. When the basal diet was deficient in Met and Cys (Experiment 1), addition of DLM or HMB had little effect on hepatic BHMT- or MS-dependent HCY remethylation, although remethylation through both pathways was reduced (P < 0.05) by the 0.11% addition of DLM, compared with 0.03% DLM or 0.04% HMB (Table 2). Similarly, when the basal diet was deficient only in Met (Experiment 2), addition of DLM or HMB had little effect on HCY remethylation through either pathway, with the exception of BHMT-dependent HCY remethylation for birds fed the basal diet without any dietary additions, which was substantially higher (P < 0.5) than any other treatment (Table 3). These data indicate that, with the exception of the dietary condition of substantial Met deficiency combined with Cys adequacy, in young broilers, dietary SAA status does not have a great effect on HCY remethylation.
In contrast to SAA level, addition of CHOL and BET resulted in substantial changes in hepatic MS-dependent HCY remethylation (Tables 2 and 3). In Experiment 1, in which the basal diet was deficient only in Met, addition of CHOL and BET resulted in substantially increased (P < 0.05) MS-dependent HCY remethylation, with the exception of the addition of CHOL to diets containing 0.04% HMB (Table 2). Similarly, in Experiment 2, in which the basal diet was deficient only in Met, addition of CHOL and BET resulted in large increases (P < 0.05) in MS-dependent remethylation (Table 3). The response to supplemental CHOL, and especially BET, appeared to be greater when the diet contained adequate Cys, and, in both experiments, the overall response of MS-dependent remethylation to BET was greater (P < 0.05) than CHOL (Tables 2 and 3). In mammals, diets containing excess Cys combined with deficient or adequate levels of Met have been shown to decrease transsulfuration (Finkelstein and Mudd, 1967; Finkelstein, 1974; Finkelstein et al., 1988), with the decrease in enzyme activity most likely being modulated by a decrease in cystathionine ß-synthase (Figure 1) activity through reduced mRNA (Yamamoto et al., 1995). The net result is an increase in the ratio of HCY transmethylation to transsulfuration (Finkelstein et al., 1988), which should lead to more HCY being utilized for Met synthesis. Therefore, the effect of Cys on total HCY remethylation (Tables 2 and 3) was not surprising.
Hepatic remethylation of HCY by BHMT was only slightly affected by CHOL or BET addition in Experiments 1 and 2 (Tables 2 and 3). When the basal diet was deficient in Met and Cys (Experiment 1), addition of CHOL or BET to the basal diet or diets containing supplemental DLM resulted in slight numeric or significant (P < 0.05) increases in BHMT-dependent HCY re-methylation; no change (P > 0.05) was observed with addition of CHOL or BET to diets containing HMB (Table 2). In Experiment 2, addition of CHOL or BET to the basal diet substantially reduced (P < 0.05) BHMT-dependent HCY remethylation, but addition of CHOL or BET to the remaining diets resulted in slight numeric or significant (P < 0.05) increases in BHMT-dependent HCY remethylation (Table 3).
The different magnitudes of response for MS- and BHMT-dependent HCY remethylation are reflected in changes in the percentage of HCY that was remethylated by BHMT (Tables 2 and 3). In both experiments, the basal diet condition resulted in the greatest (P < 0.05) percentage of HCY remethylation by BHMT, and the value was considerably higher when the basal diet contained adequate Cys (Experiment 2). The percentage of HCY that was remethylated by BHMT was reduced (P < 0.05) to a similar degree to DLM and HMB, and values were remarkably similar in Experiments 1 and 2. A further reduction (P < 0.05) in the proportion of BHMT-dependent HCY remethylation occurred with the addition of CHOL and BET; the degree of reduction was slightly greater in Experiment 2, reflecting the larger magnitude of change in MS-dependent HCY remethylation that occurred in Experiment 2. It should be noted that, with the exception of the basal diet in Experiment 2, the effect of CHOL and BET on the proportion of HCY that was remethylated by BHMT was not the result of reduced flux through this pathway but rather of the proportionately greater increased flux through the MS pathway.
In these experiments, MS-dependent remethylation clearly predominated and appeared to be more responsive to dietary changes, perhaps suggesting a regulatory role for MS in young broilers fed diets deficient in Met and Cys or Met alone. These data agree with previous research (Pillai et al., 2006) that indicated a more substantial role for MS-dependent HCY remethylation in young broilers fed diets deficient in Met and Cys. Similar to the current experiment, they observed a lack of remethylation response to SAA level and an increased level of MS-dependent remethylation in response to CHOL and BET addition.
Based on enzyme activity, most studies suggest a greater role for BHMT in remethylation, especially under conditions of dietary Met deficiency or when surfeit CHOL or BET are present. Finkelstein et al. (1982) observed increased hepatic BHMT activity when rats were fed diets devoid of Met or containing excess protein or Met, in the presence of adequate Cys. Studies with rats indicated that BHMT activity increases when surfeit CHOL or BET is added to a diet adequate in Cys and deficient in Met (Finkelstein et al., 1982; Park et al., 1997; Park and Garrow, 1999). Saunderson and Mackinlay (1990) reported that activity of BHMT was higher than that of MS in avian liver, and Met-deficient conditions resulted in increased hepatic BHMT activity. Emmert et al. (1996) reported that hepatic BHMT activity increased in response to addition of surfeit CHOL or BET to diets deficient in Met and Cys; the response to surfeit CHOL or BET was amplified by the simultaneous addition of Cys.
In the current research, in which actual HCY flux was assessed, hepatic BHMT did not appear to be responsible for conservation of cellular Met levels under dietary conditions that, based on previous research, would be expected to increase hepatic BHMT activity. In contrast, MS appeared to be the enzyme responsible for the majority of HCY remethylation under most dietary conditions. This agrees with our previous research (Pillai et al., 2006) but is somewhat surprising in light of research with rats and humans that suggested HCY remethylation is partitioned fairly evenly between the 2 pathways (Mudd et al., 1970; Finkelstein and Martin, 1984). Interestingly, BHMT-dependent HCY remethylation was 48.2% under the basal dietary conditions in Experiment 1 (Table 2), in which the diet was deficient in Met and Cys, and Pillai et al. (2006) reported a BHMT-dependent remethylation value of 48.3% for birds fed diets containing a roughly adequate level of Met and Cys.
The actual mechanism behind the effect of surfeit dietary CHOL or BET on hepatic HCY remethylation through MS pathway is not clearly elucidated, but 1 of the by-products of BHMT-dependent remethylation is N,N-dimethylglycine, which is a feedback inhibitor of BHMT (Stipanuk, 2004). Perhaps, with diets containing deficient Met and surfeit CHOL or BET (which have been shown to increase BHMT activity in chicks; Emmert et al., 1996), the increased flux that would be expected from higher activity is prevented by feedback inhibition from N,N-dimethylglycine. Further, sarcosine, which is a product of oxidative demethylation of N,N-dimethylglycine, may be providing methyl groups to the folate pool, which are then made available for MS-dependent HCY remethylation.
Because of the mixing error in Experiment 1, an efficacy estimate for HMB cannot be calculated. However, the similarity in growth performance of birds fed 0.03% DLM and 0.04% HMB (Table 2) suggests no substantial difference in efficacy. In Experiment 2, results from multiple linear regression analysis can be used to calculate efficacy values, which were 81.3, 79.1 (P < 0.05), and 74.0% (P < 0.08) for diets containing no addition, surfeit CHOL, or surfeit BET, respectively. Efficacy values did not appear to be affected to a substantial degree by CHOL or BET, indicating that increased HCY remethylation, which occurred in diets containing surfeit CHOL or BET, was not correlated with differences in HMB efficacy.
The efficacy of HMB as source of Met is still being debated after years of intensive research. Many researchers have reported lower bioavailability estimates for HMB (van Weerden et al., 1983; Thomas et al., 1991; Huyghebaert, 1993; Rostagno and Barbosa, 1995; Lemme et al., 2002), whereas others have reported no difference in bio-availability in broilers (Knight and Dibner, 1984; Römer and Abel, 1999; Daenner and Bessei, 2003). These conflicting observations may be the result of differences in the basal Met levels in diets, the presence or absence of Cys and its adequacy in the diet, the ratio of Met to Cys, the level of CHOL or lecithin in the diet, and, finally, the species and age of the animal (Schreiner and Jones, 1987). Also, the differences in efficacy estimates may be due to production of nonabsorbable, non-Met products in the gastrointestinal tract (Maenz and Engele-Schaan, 1996) or even the acid–base balance of the diets (Saroka and Combs, 1986).
In conclusion, addition of CHOL or BET to diets marginally deficient in SAA resulted in a marginal increase in weight gain in broiler chicks, but the response was inconsistent. Also, addition of CHOL or BET to diets that were deficient in Met and Cys or Met alone resulted in increased total remethylation, and the magnitude of HCY remethylation associated with CHOL or BET addition was greater in diets deficient only in Met. The proportion of remethylation through BHMT was reduced by addition of either DLM or HMB and was further lowered by addition of CHOL and BET. Choline and BET appeared to have a higher effect on MS-dependent HCY remethylation than BHMT-dependent remethylation, and the overall contribution of MS to HCY remethylation was much greater than that expected under most conditions. With fairly similar remethylation responses to CHOL or BET but only isolated differences in the growth response, it does not appear that HCY remethylation is highly correlated with growth under the dietary conditions used herein.
Received for publication February 2, 2006. Accepted for publication May 30, 2006.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Cao, Z., H. Cai, and C. N. Coon. 1995. Methionine and cystine requirements and metabolism for layers and broilers. Pages 257–289 in Proc. Minn. Nutr. Conf., Bloomington, MN. Univ. Minn. Extension Serv., St. Paul, MN.
Daenner, E., and W. Bessei. 2003. Influence of supplementation with liquid DL-methionine hydroxy analogue-free acid (Alimet) or DL-methionine on performance of broilers. J. Appl. Poult. Res. 12:101–105.
Emmert, J. L., T. A. Garrow, and D. H. Baker. 1996. Hepatic betaine-homocysteine methyltransferase activity in the chicken is influenced by dietary intake of sulfur amino acids, choline, and betaine. J. Nutr. 126:2050–2058.
Emmert, J. L., D. M. Webel, R. R. Biehl, M. A. Griffiths, L. S. Garrow, T. A. Garrow, and D. H. Baker. 1998. Hepatic and renal betaine-homocysteine methyltransferase activity in pigs as affected by dietary intakes of sulfur amino acids, choline, and betaine. J. Anim. Sci. 76:606–610.
Esteve-Garcia, E., and L. L. Llauradó. 1997. Performance, breast meat yield and abdominal fat deposition of male broiler chickens fed diets supplemented with DL-methionine or DL-methionine hydroxy analogue free acid. Br. Poult. Sci. 38:397–404.[Web of Science][Medline]
Esteve-Garcia, E., and S. Mack. 2000. The effect of DL-methionine and betaine on growth performance and carcass characteristics in broilers. Anim. Feed Sci. Technol. 87:85–93.
Finkelstein, J. D. 1974. Methionine metabolism in mammals: The biochemical basis for homocystinuria. Metabolism 23:387–398.[Web of Science][Medline]
Finkelstein, J. D., B. J. Harris, J. J. Martin, and W. E. Kyle. 1982. Regulation of hepatic betaine-homocysteine methyltransferase by dietary methionine. Biochem. Biophys. Res. Commun. 108:344–348.[Web of Science][Medline]
Finkelstein, J. D., W. E. Kyle, and B. J. Harris. 1971. Methionine metabolism in mammals. Regulation of homocysteine methyltransferases in rat tissue. Arch. Biochem. Biophys. 146:84–92.[Web of Science][Medline]
Finkelstein, J. D., and J. J. Martin. 1984. Methionine metabolism in mammals. Distribution of homocysteine between competing pathways. J. Biol. Chem. 259:9508–9513.
Finkelstein, J. D., J. J. Martin, and B. J. Harris. 1988. Methionine metabolism in mammals. The methionine-sparing effect of cystine. J. Biol. Chem. 263:11750–11754.
Finkelstein, J. D., and S. H. Mudd. 1967. Transsulfuration in mammals: The methionine-sparing effect of cystine. J. Biol. Chem. 242:873–880.
Garlich, J. D. 1985. Response of broilers to DL-methionine hydroxy analog free acid, DL-methionine, and L-methionine. Poult. Sci. 64:1541–1548.[Web of Science][Medline]
Huyghebaert, G. 1993. Comparison of DL-methionine and methionine hydroxy analogue-free acid in broilers by using multi-exponential regression models. Br. Poult. Sci. 34:351–359.[Web of Science]
Knight, C. D., and J. J. Dibner. 1984. Comparative absorption of 2-hydroxy-4-(methylthio)-butanoic acid and L-methionine in the broiler chick. J. Nutr. 114:2179–2186.
Lemme, A., D. Hoehler, J. J. Brennan, and P. F. Mannion. 2002. Relative effectiveness of methionine hydroxy analog compared to DL-methionine in broiler chickens. Poult. Sci. 81:838–845.
Lowry, K. R., O. A. Izquiredo, and D. H. Baker. 1987. Efficacy of betaine relative to choline as a methyl donor. Poult. Sci. 66(Suppl. 1):135.
Maenz, D. D., and C. M. Engele-Schaan. 1996. Methionine and 2-hydroxy-4-methylthiobutanoic acid are partially converted to nonabsorbed compounds during passage through the small intestine and heat exposure does not affect small intestinal absorption of methionine sources in broiler chicks. J. Nutr. 126:1438–1444.
Mudd, S. H., J. D. Finkelstein, F. Irreverre, and L. Laster. 1965. Transsulfuration in mammals: Microassays and tissue distributions of three enzymes of the pathway. J. Biol. Chem. 240:4382–4392.
Mudd, S. H., H. Levy, and G. Morrow III. 1970. Deranged B12 metabolism: Effects on sulfur amino acid metabolism. Biochem. Med. 4:193–214.[Web of Science][Medline]
Muramatsu, T., H. Yokota, J. Okumura, and I. Tasaki. 1984. Biological efficacy of liquid methionine and methionine hydroxy analogue-free acid in chicks. Poult. Sci. 63:1453–1456.[Web of Science][Medline]
National Research Council. 1994. Nutrient Requirements of Poultry. 9th ed. Natl. Acad. Press, Washington, DC.
Park, E. I., and T. A. Garrow. 1999. Interaction between dietary methionine and methyl donor intake on rat liver betaine-homocysteine methyltransferase gene expression and organization of the human gene. J. Biol. Chem. 274:7816–7824.
Park, E. I., M. S. Renduchintala, and T. A. Garrow. 1997. Diet-induced changes in hepatic betaine-homocysteine methyl-transferase activity are mediated by changes in the steady-state level of its mRNA. J. Nutr. Biochem. 8:541–545.[Web of Science]
Pesti, G. M., A. E. Harper, and M. L. Sunde. 1980. Choline/methionine nutrition of starting broiler chicks. Three models for estimating the choline requirement with economic considerations. Poult. Sci. 59:1073–1081.[Web of Science][Medline]
Pillai, P. B., A. C. Fanatico, K. W. Beers, M. E. Blair, and J. L. Emmert. 2006. Homocysteine remethylation in young broilers fed varying levels of methionine, choline, and betaine. Poult. Sci. 85:90–95.
Quillin, E. C., G. F. Combs, R. D. Creek, and G. L. Romoser. 1961. Effect of choline on the methionine requirements of broiler chickens. Poult. Sci. 40:639–645.
Römer, A., and H. J. Abel. 1999. Effects of DL-methionine hydroxyl analogue (MHA) or DL-methionine (DL-Met) on N-retention in broiler chickens and pigs. Anim. Feed Sci. Technol. 81:193–203.
Rostagno, H. S., and W. A. Barbosa. 1995. Biological efficacy and absorption of DL-methionine hydroxy analogue free acid compared to DL-methionine in chickens as affected by heat stress. Br. Poult. Sci. 36:303–312.[Web of Science][Medline]
Rostagno, H. S., and M. Pack. 1996. Can betaine replace supplemental DL-methionine in broiler diets? J. Appl. Poult. Res. 5:150–154.
Saroka, J. M., and G. F. Combs Jr. 1986. Studies of the renal excretion of the hydroxyl analogue of methionine by the chick. Poult. Sci. 65:1375–1382.[Web of Science][Medline]
SAS Institute. 2004. SAS/STAT User’s Guide: Statistics. Version 9.2. SAS Inst. Inc., Cary, NC.
Sasse, C. E., and D. H. Baker. 1973. Availability of sulfur amino acids in corn and corn gluten meal for growing chicks. J. Anim. Sci. 37:1351–1355.
Saunderson, L., and J. Mackinlay. 1990. Changes in bodyweight, composition, and hepatic enzyme activities in response to dietary methionine, betaine and choline levels in growing chicks. Br. J. Nutr. 63:339–349.[Web of Science][Medline]
Schreiner, C. L., and E. E. Jones. 1987. Metabolism of methionine and methionine hydroxy analogue by porcine kidney fibroblasts. J. Nutr. 117:1541–1549.
Schutte, J. B., J. De Jong, W. Smink, and M. Pack. 1997. Replacement value of betaine for DL-methionine in male broiler chicks. Poult. Sci. 76:321–325.
Simon, J. 1999. Choline, betaine and methionine interactions in chickens, pigs and fish (including crustaceans). World’s Poult. Sci. J. 55:353–374.
Stipanuk, M. H. 2004. Sulfur amino acid metabolism: Pathways for production and removal of homocysteine and cysteine. Annu. Rev. Nutr. 24:539–577.[Web of Science][Medline]
Storch, K. J., D. A. Wagner, J. F. Burke, and V. R. Young. 1988. Quantitative study in vivo of methionine cycle in humans using [methyl-2H3]- and [1-13C]methionine. Am. J. Physiol. 255:E322–E331.[Medline]
Storch, K. J., D. A. Wagner, and V. R. Young. 1991. Methionine kinetics in adult men: Effects of dietary betaine on L-[2H3-methyl-1-13C]methionine. Am. J. Clin. Nutr. 54:386–394.
Thomas, O. P., C. Tamplin, S. D. Crissey, E. Bossard, and A. Zuckerman. 1991. An evaluation of methionine hydroxy analog free acid using a nonlinear (exponential) bioassay. Poult. Sci. 70:605–610.[Web of Science]
van Guldener, C., W. Kulik, R. Berger, D. A. Dijkstra, C. Jakobs, D. J. Reijngoud, A. J. M. Donker, C. D. A. Stehouwer, and K. de Meer. 1999. Homocysteine and methionine metabolism in ESRD: A stable isotope study. Kidney Int. 56:1064–1071.[Web of Science][Medline]
van Weerden, E. J., J. B. Schutte, and H. L. Bertram. 1983. DL-Methionine and DL-methionine hydroxy analogue free acid in broiler diets. Poult. Sci. 62:1269–1274.
Vazquez-Anon, M., E. Saleh, S. Peak, T. Hampton, C. Lopez-Coello, J. Firman, and C. Knight. 2003. Effect of 2-hydroxy-4(methylthio) butanoic acid (HMB) and DL-methionine in sorghum-soybean meal diets on broiler performance. Poult. Sci. 82(Suppl. 1):29.
Virtanen, E., and G. Rumsey. 1996. Betaine supplementation can optimize use of methionine, choline in diets. Feedstuffs 68:12–13.
Waldroup, P. W., C. J. Mabray, J. R. Blackman, P. J. Slagter, R. J. Short, and Z. B. Johnson. 1981. Effectiveness of the free acid of methionine hydroxy analogue as a methionine supplement in broiler diets. Poult. Sci. 60:438–443.[Web of Science][Medline]
Xue, G., and A. M. Snoswell. 1985. Comparative studies on methionine synthesis in sheep and rat tissues. Comp. Biochem. Physiol. B 80:489–494.[Medline]
Yamamoto, N., T. Tanaka, and T. Noguchi. 1995. Effect of cysteine on expression of cystathionine ß-synthase in the rat liver. J. Nutr. Sci. Vitaminol. (Tokyo) 41:197–205.[Medline]
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
-lyase; 6) N5,N10-methylenetetrahydrofolate reductase; 7) Met synthase; 8) CHOL dehydrogenase; 9) BET aldehyde dehydrogenase; and 10) BET–HCY methyltransferase.