Cysteines and Methionines

Figure 2.5 The cisplatin reactive group can covalently couple to methionine-, cysteine-, and histidine-containing peptides or proteins. It also reacts with guanine groups to form a covalent modification on the N7 nitrogen.

AC Fernandez-Trapiella. Quantitative analysis of methionine, cysteine, and lysine in feeds by... 

It is of note that alkaline and acid phosphatase exhibit no silikatase activity. Divalent sulfur-containing compounds, such as sulfide, methionine, cysteine and glutathione have a positive effect on silica uptake536) also water temperature and silica concentration in the aqueous phase control the Si-cycle in cellular systems529-531, 53 ). 

Other workers (309) have extended this reaction and found that mixtures of a-amino acids (glycine, alanine, phenylalanine, tyrosine, tryptophan, leucine, methionine, cysteine) and benzil when heated to 180-220° gave good yields of 2,3,5,6-tetraphenylpyrazine, and a mechanism also involving an a-amino ketone was proposed. Benzoin with glycine, alanine, phenylalanine, or tyrosine at elevated temperatures similarly gave tetraphenylpyrazine. 

Reactions of Methionine, Cysteine and Cystine. Determination of Methionine by Hydrogen Peroxide Oxidation. J. biol. Chem. 129, 48l (1939). 

Preston BD, Miller JA, Miller EC. 1984. Reactions of 2,2, 5,5 -tetrachlorobiphenyl-3,4-oxide with methionine, cysteine and glutathione in relation to the formation of methylthio-metabolites of 2,2, 5,5 -tetrachlorobiphenyl in the rat and mouse. Chem-Biol Ineract 50 289-312. 

Nielsen, H. K., Finot, P. A., and Hurrell, R. F., Reactions of proteins with oxidizing lipids. 1. Influence of protein quality on the bioavailability of lysine, methionine, cysteine, and tryptophan as measured in rat assays, Br. ]. Nutr., 53, 75, 1985. 

The breakdown of protein and amino acids in the intestinal tract and their enzymatic hydrolysis in cells releases sulfur from sulfur-containing proteins. The biological importance of sulfur partly involves the amino acids methionine, cysteine and taurine, and other metabolites such as glutathione and N-acetyl-methionine. Hence, sulfur plays biochemical and physiological... 

When examining the protein quality of other soy products, such as SPC (approximately 64% protein) and SPI (approximately 85% protein), compared with SBM, both similarities and differences are found. SPC and SPI are first-limiting in methionine + cysteine and second-limiting in threonine, the same as for SBM. The overall protein quality of SPI, however, is lower than that of SBM (Emmert Baker, 1995), which is due to the lower concentrations of total and digestible methionine + cysteine and threonine in the protein of the SPI than in the protein of SBM or SPC (Emmert... 

Oxidation in proteins and peptides are highly amino acid specific. The amino acid residues that are susceptible to oxidation generally fall into two groups, viz. those containing a sulphur atom (methionine, cysteine) and those with an aromatic side chain (histidine, tryptophan and tyrosine) [49]. 

Fig. 4. Dose-dependence of US2-mediated degradation of HLA-DR in cells differing in DR expression. His 16 or HeLa cells transiently transfected with plasmids encoding DR-a or DR-p were infected for 18h with AdtetUS2, and then cells were labeled for 3h with S-methionine/cysteine and HLA-DR immu-noprecipitated. Quantification by phosphoimager analyses indicated that His 16 cells expressed 20- to 40-fold more DR than was expressed in transfected HeLa cells, and the levels of US2 expressed at each dose of AdtetUS2 were very similar. US2 at any given concentration was equally able to cause degradation of DR-a in transfected HeLa cells and in His 16 cells. DR-a was degraded in the absence of DR-p...

The biosynthesis of simple amines appears to involve a single enzyme with broad specificity. An enzyme with this activity, isolated from red algae (Rhodophyceae), was capable of decarboxylation of the L-forms of leucine, valine, isoleucine, norvaline, 2-aminobutyric acid, phenylalanine, methionine, cysteine, and homocysteine. A number of other amino acids were unable to serve as precursors (Smith, 1980). 

One of the major chemical properties of the phenolic acids is the ease with which they oxidize. In the presence of oxygen, chlorogenic acid, caffeic acid and other related o-diphenols can oxidize by the action of polyphenol oxidase or in alkaline solution. These polyphenol oxidases are copper-containing proteins and are widespread in nature. Some of them oxidize only selected o-dihydroxyphenols while others, such as tyrosinase, not only oxidize dihydroxyphenols but convert monohydroxyphenols, such as tyrosine, to oxidizable dihydroxyphenols. The quinones formed are highly reactive substances which normally react further with other quinones to produce coloured compounds of high molecular weight. They may also react however with lysine, methionine, cysteine and tryptophan residues in the protein chain (Fig. 1). 

The reaction of quinones with amino acids and proteins was reviewed by Mason (1955). A more recent study of the reaction of enzymatically generated caffeoquinone and chlorogenoquinone with amino acids and proteins was made by Pierpoint (1969ab, 1971). The sulphydryl groups of cysteine and the e-amino groups of lysine as well as a-terminal amino acid groups appear to coirr-bine most readily with quinones. Methionine (Vithayathil and Murphy, 1972 Bosshard, 1972) and tryptophan (Synge, 1975) could also react and, in addition methionine, cysteine and tryptophan... 

Flow wash the resin for 30 s with DCM to remove excess DMF. Close the stopcock and add sufficient TFA (neat) to the resin to allow fluid motion of the resin when agitated. Replace the cap and apply rotation. Deprotect for 1 min and open the stopcock remove the TFA. Avoid sucking excess air through the resin, particularly with peptides with oxygen sensitive moieties (e.g., methionine, cysteine, and thioesters). 

Chemical modification of amino acid side chain functionalities will also serve to cleave specific peptide bonds selectively. Chemical cleavage of a polypeptide chain exploits the unique reactivity of chemically modified side chains of particular amino acids in the labilization of adjacent peptide bonds by neighbouring group participation (68). The residues investigated so far for this purpose have been methionine, cysteine and the aromatic amino acids including tryptophan (438-440, 443). 

Dye-sensitized photooxidation with visible light to identify residues critically involved in the biological activity of enzymes has been introduced by Weil et al. (425). The procedure is mild and moderately selective for some amino acid side chains in addition to tryptophan, tyrosine, histidine, methionine, cysteine and cystine are also photooxidizable. It has been found possible, by an appropriate choice of dye, to bring about specific modification of a particular residue. There is, however, considerable variation in the effects of different dyes and of particular experimental conditions [see ref. 112, 255, 319, 426) for reviews]. 

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