Methionine protein

Primary and secondary products, and end-products of lipid peroxidation have all been shown to accumulate in senile cataracts (Babizhayev, 1989b Simonelli et al., 1989). Accumulation of these compounds in the lenticular epithelial membranes is a possible cause of damage preceding cataract formation. In senile cataracts there is also extensive oxidation of protein methionine and cysteine in both the membrane and cytosol components (Garner and Spector, 1980), while in aged normal lenses a lesser extent of oxidation was confined to the membrane. The authors therefore suggested that oxidation of membrane components was a precataract state. 

This reductase, officially known as protein-methionine- -oxide reductase [EC 1.8.4.6], catalyzes the reaction of protein L-methionine with oxidized thioredoxin to yield protein L-methionine -oxide and reduced thioredoxin. Dithiothreitol can replace reduced thioredoxin in the reverse reaction. Free methionine is not a substrate however free methionine is similarly acted upon by an analogous reductase [EC 1.8.4.5]. 

Structural studies95-97,101 103 on cytochromes of the c and c2 types show that the heme group provides a core around which the peptide chain is wound. The 104 residues of mitochondrial cytochrome c are enough to do little more than envelope the heme. In both the oxidized and reduced forms of the protein, methionine 80 (to the left in Fig. 16-8A) and histidine 18 (to the right) fill the axial coordination positions of the iron. The heme is nearly "buried" and inaccessible to the surrounding solvent. 

Altenbach, S.B., Kuo, C.C., Staraci, L.C. et al. 1992. Accumulation of a Brazil nut albumin in seeds of transgenic canola results in enhanced levels of seed protein methionine. Plant Mol Biol 18 235-245. 

Besides being incorporated into proteins, methionine is the source of methyl groups for several important reactions, including the modification of cellular RNAs and the biosynthesis of lipids. 

In tertiary structures of proteins, methionine residues differ with respect to their exposure to oxidizing agents and the protective effect of their intramolecular... 

Gallium can interfere with the structural integrity of transferrin, the ircin-binding protein that transports iron in the serum. Gallium is believed to bind in the protein methionine. In microorganisms like Escherichia coli, gallium suppresses the synthesis of low-molecular weight polypeptides. It also concentrates on the surface of the cell envelope. 

Modgil, R. and Mehta, U. 1994. Effects of different levels of Collosobruchus chinensis L. infestation on proximate principles, true protein, methionine and uric acid contents of greengram and redgram. 

From the observations described here and other reports in the literature (Fowler and Bennett, 1984 Broschat and Burgess, 1986 Heald and Hitchcock-DeGregori, 1988), there does not appear to be a direct cause-and-effect relationship between propensity for head-to-tail polymerizahon and affinity of actin binding. There may be several reasons for this, including a less than satisfactory experimental method for measuring head-to-taU interaction. Viscosity measurements can only be considered a qualitative tool for this purpose and are subject to major uncertainties in their experimental application. Clearly a more reliable experimental method is needed. The methodology by which the TM is prepared may also have significant effects on the polymerization properties of the protein. Methionines, of which there are three in residues... 

For human beings methionine is nutritionally essential and comes entirely from the diet. ITowever, the oxoacid analog of methionine can be used as a nutritional supplement. Dietary homocysteine can also be converted into methionine to a limited extent. Methionine is incorporated into proteins as such and as N-formylmethionine at the N-terminal ends of bacferial profeins (steps a and b, Fig. 24-16). In addition to its function in proteins methionine plays a major role in biological methylation reactions in all organisms. It is converted into S-adenosylmethionine (AdoMet or SAM Fig. 24-16, step e see also Eq. 17-37), ° ° which is the most widely used methyl group donor for numerous biological methylation reactions (Eq. 12-3). S-Adenosylmethionine is also the precursor of the special "wobble base" queuine (Fig. 5-33). The product of transmethylation, S-adenosylhomocysteine, is converted (step... 

Myeloperoxidase contains two Fe heme-like centers, which give it the green color seen in pus. Hypochlorous acid is a powerful toxin that destroys bacteria within seconds through halogenation and oxidation reactions. It oxidizes many Fe and S-containing groups (e.g., sulfhydryl groups, iron-sulfur centers, ferredoxin, heme-proteins, methionine), oxidatively decarboxylates and deaminates proteins, and cleaves peptide bonds. Aerobic bacteria under attack rapidly lose membrane... 

In contrast, methylcobalamin-dependent reactions, which include methionine synthase, and anaerobic methyl transferases found in acetogens and methanogens, appear to involve heterolysis of the cobalt-methyl bond. In the best studies of these proteins, methionine synthase, the B12 cofactor, serves as an intermediate in the shuttling of a methyl group equivalent (CH3+) from methyl tetrahydrofolate to homocysteine in the final step of the biosynthetic pathway of... 

Most of the inorganic sulfate assimilated and reduced by plants appears ultimately in cysteine and methionine. These amino acids contain about 90% of the total sulfur in most plants (Allaway and Thompson, 1966). Nearly all of the cysteine and methionine is in protein. The typical dominance of protein cysteine and protein methionine in the total organic sulfur is illustrated in Table I by analyses of the sulfur components of a lower plant (Chlorella) and a higher plant (Lemna). Thede novo synthesis of cysteine and methionine is one of the key reactions in biology, comparable in importance to the reduction of carbon in photosynthesis (Allaway, 1970). This is so because all nonruminant animals studied require a dietary source of methionine or its precursor, homocysteine. Animals metabolize methionine via cysteine to inorganic sulfate. Plants complete the cycle of sulfur by reduction of inorganic sulfate back to cysteine and methionine, and are thus the ultimate source of the methionine in most animal diets (Siegel, 1975). 

In the nonprotein fraction reduced glutathione, GSH, is ubiquitous, and is commonly a mqjor constituent (Table I). The soluble fraction of plants also includes a variety of other sulfur-containing compounds that are normally present in relatively small amounts (a) Intermediates on the route to protein cysteine and protein methionine, such as cysteine, cystathionine, homocysteine, and methionine, (b) Compounds involved in methyl transfer reactions and polyamine synthesis AdoMet.t AdoHcy, and, presumably, 5 -methyl-thioadenosine. The biochemistry of the compounds in both groups (a) and (b) will be discussed here, (c) Compounds clearly related metabolically to cysteine or methionine, such as 5-methylcysteine and 5-methylmethionine. Because in certain plants these derivatives comprise a major portion of the nonprotein sulfur amino acids, they will be discussed here, (d) A number of compounds of uncertain function, the biochemistry of which has often not been clarified. Discussion of such compounds (Richmond, 1973 Fowden, 1964) is beyond the scope of this chapter. 

Total organic sulfur = protein cysteine + protein methionine + soluble sulfur compounds - S04. ... 

Multiplication by this factor converts listed values of a compound (in nmolesZ/smol protein methionine) to estimates of concentrations UtM), assuming uniform distribution of the compound throughout the idant. For example the concentration of AdoMet in Lemna growing at... 

In addition to its role in the synthesis of proteins, methionine, as the 5 -adenosyl derivative, acts as a methyl donor in a wide variety of biosynthetic reactions. As shown in Figure 11.22, the resultant homocysteine may either be metabolized to yield cysteine or may be remethylated to yield methionine. 

By far the most common control pattern for biosynthetic pathways is by feedback regulation by the product or products of the pathway. Dougall (1965) reported that Paul s Scarlet Rose cells growing in the presence of [ Cjglucose and methionine synthesized only 20% of the carbon atoms of protein methionine... 

Cysteine is the starting point for the synthesis of many other compounds, including the cysteinyl residues of proteins, methionine, and glutathione. It is also the starting point for the synthesis of many secondary compounds though these processes are not regarded as essential and are not discussed in this article. This section is concerned with mechanisms which degrade cysteine and thereby... 

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