Methionine nutrition effect

Nutritional Effects of Oxidized Sulfur Amino Acids. In 1937, Bennett (59, 60, 61, 62) already showed that the different oxidation products of methionine and cystine did not have the same biological effects to promote the growth of rats fed on diets deficient in sulfur-containing amino acids. Methionine sulfone and cysteic acid did not promote growth while the lower oxidation products had a positive effect and could replace methionine and cystine to a certain extent (see Table I). 

Nutrition Effect of Protein-Bound Methionine Sulfoxide. There is some discrepancy in the results concerning the biological availability of protein-bound methionine sulfoxide. Ellinger and Palmer (71) found that oxidized casein had a lower NPU (Net Protein Utilization) than normal casein. Slump and Schreuder (72) concluded that there was a positive biological availability of peptide-bound methionine sulfoxide. 

By the 1930s many workers had shown that nutritionally inadequate proteins, such as zein from maize, could be effective as a source of nitrogen if supplemented by additional amino acids (for zein, tryptophan). Even if it contained all the essential amino acids, the amount of protein in the diet influenced the results. Osbome and Mendel found that if the diet contained 18% by weight casein, which is low in cystine, young rats grew, but if the amount of protein was diminished, added cystine was required to offset the relative deficiency of this amino acid. Later, after methionine had been discovered, it was shown to replace the need for cystine. 

Although in humans only MsrBl is a selenoprotein, the depletion of selenium from the diet of mice led to increases in both R and S stereoisomers. This was not initially explained, yet a subsequent study has shown that small molecule selenols (organic selenocysteine homologues) could act as efficient electron donors in vitro for MsrA enzymes. ° This effect has only been shown in vitro, but the possibility that small molecular selenium reductants, or more likely that some selenoproteins that contain reduced selenols (in redox-active motifs) is quite intriguing. Several small selenoproteins do not have real roles and reside in nearly all subcompartments of the cell (mitochondria, ER) where electron donors for Msr enzymes are probably critical to maintain protein stability. Low selenium nutritional status would then have a significant impact on all methionine oxidation, as Future studies to address selenium nutrition and methionine oxidation could prove to be... 

Nutrition may have a considerable effect. A high intake of milk protein in neonates will result in an increase in most plasma amino acids, especially methionine and tyrosine. Canned infant formulae may contain homocitrulline, which may appear in the patient s urine. White meat (chicken ) will contain carnosine, anserine, and... 

Excessive heat can cause destruction of amino acid residues. The amino acid most susceptible to direct heat destruction is cystine. Although not an essential amino acid, cystine does have a sparing effect on the dietary requirement for methionine. As a result, cystine destruction can be nutritionally important. In addition, many vegetable proteins are limiting in the sulfur amino acids. Cystine destruction would be particularly harmful for these proteins. 

In addition to cytochrome P-450 induction, other diet induced metabolic effects are likely to be involved in carcinogenesis. High temperature processing or long-term storage of foods with attendant exposure to oxygen can lead to the formation of lipid peroxides and oxidized sulfur amino acids in the food. The partially oxidized S-amino acids cystine monoxide (CMO) and methionine sulfoxide (MSO) are nutritionally available, but require in vivo conversion to the reduced amino acids at the... 

More details of the chemical modification of casein and other food proteins with carboxyl-amino acid anhydrides will be published elsewhere. Depending on the distribution and length of copolymers of methionine covalently linked to proteins, distinct effects on functional and nutritional properties of the modified proteins are expected. 

Our results have been recapitulated with other proteins of varying nutritional value to S. exigua and H. zea they include soy protein, tomato foliar protein, corn gluten and zein. In all cases, more than 2.5% dietary protein was required to alleviate antinutritional effects, because these proteins are less nutritious than casein (Table III). The ability of a protein to alleviate the toxicity of o-quinones is proportional to its nutritional value to the insect (Table III). The proteins ability to function as an alkylatable sink (alleviation of antinutritive effects) is correlated with the relative amounts of alkylatable amino acids (e.g., lysine, cysteine, histidine, methionine Felton and Duffey, unpublished data). 

When amino acids in parenteral solutions are exposed to relatively intense illumination for 24 hours, simulating phototherapy in neonatal nurseries, most individual amino acids decrease only slightly. Decreases in the concentrations of methionine, proline, tryptophan, and tyrosine are significantly greater in the presence of riboflavine. The observed decreases in amino acid concentrations are unlikely to be nutritionally important. However, in view of the possibility that photooxidation products may exert toxic effects, it is best to shield amino acid solutions containing vitamins from strong sources of UV-VIS irradiation (86). 

E. Hunter and R. Grimble, Cysteine and Methionine Supplementation Modulate the Effects of TNF-a on Protein Synthesis, Glutathione and Zinc Content of Liver and Lung in Rats Fed a Low Protein Die, J Nutrition 124 (1994) 2319-2328. 

It is true that when the selenium and/or methionine in the diet is suboptimum, there is a marked increase in the requirement for vitamin E. However, many stresses and other nutritional deficiencies are also known to increase the tocopherol requirement. For example, carbon tetrachloride toxicity, protein, B12 and folic acid deficiencies (Hove and Hardin, 1951a,b), and Be deficiency (Day and Dinning, 1956), all increase the requirement for a-tocopherol. As for the relationship of ubiquinone to tocopherol, here also, one wonders whether the decreased amount of ubiquinone found in vitamin E deficiency is specific or an incidental effect of one form of inanition, since a deficiency of pantothenic acid, and possibly other deficiencies that affect liver function, will produce similar decreases in ubiquinone. 

However, in more recent studies, Scott and Calvert (1960, 1962) found that cystine is more effective than methionine and, therefore, that cystine may be more closely related to the primary metabolic function responsible for prevention of nutritional muscular dystrophy. Representative results of these experiments are shown in Table II. Although 0.19% DL-methionine... 

Goseki, N., Yamazaki, S., Shimojyu, K., Kando, F., Maruyama, M., Endo, M., Koike, M., and Takahashi, H., 1995, Synergistic effect of methionine-depleting total parenteral nutrition with 5-fluorouracil on human gastric cancer A randomized, prospective clinical trial. Jpn. J. Cancer Res. 86 484-489. 

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