Of methionine residue

Proteins can be cleaved specifically at the amide bond on the carboxyl side of methionine residues by reaction with cyanogen bromide. BrC=N. 

TABLE 2. Proteins and peptides whose biological activity is affected by oxidation of methionine residues ... 

Ribosomal protein L12 was oxidized with 0.3 M H202 at 30°C for 1 h. After dialysis, the protein was incubated in the presence of 0.8 M 2-mercaptoethanol for 48 min at 37 °C and dialyzed. The amount of methionine residues was quantitated by exhaustive alkylation of the protein with [14C]iodoacetic acid. 

The most commonly utilized chemical cleavage agent is cyanogen bromide (it cleaves the peptide bond on the carboxyl side of methionine residues). V8 protease, produced by certain staphylococci, along with trypsin are two of the more commonly used proteolytic-based fragmentation agents. 

Alternatively, cleavage can be done chemically, but here specificity of cleavage at a single defined position is complicated, since most chemical cleavage methods react with single amino acids (Table 5.13). For instance, chemical cleavage at the C-terminal side of methionine residue can be effected using CNBr, but the use of this method is limited, since most proteins are likely to contain internal methionine residues. 

Oxidation of methionine residues involves hydrogen peroxide (H2O2)-catalyzed conversion of the terminal... 

Yin J, Chu JW, Ricci MS, Brems DN, Wang DI, Trout BL. Effects of antioxidants on the hydrogen peroxide-mediated oxidation of methionine residues in granulocyte colony-stimulating factor and human parathyroid hormone fragment 13-34. Pharm Res 2004 21 (12) 2377—2383. 

The sulfur atom of methionine residues may be modified by formation of sulfonium salts or by oxidation to sulfoxides or the sulfone. The cyanosulfonium salt is not particularly useful for chemical modification studies because of the tendency for cyclization and chain cleavage (129). This fact, of course, makes it very useful in sequence work. Normally, the methionine residues of RNase can only be modified after denaturation of the protein, i.e., in acid pH, urea, detergents, etc. On treatment with iodoacetate or hydrogen peroxide, derivatives with more than one sulfonium or sulfoxide group did not form active enzymes on removal of the denaturing agent (130) [see, however, Jori et al. (131)]. There was an indication of some active monosubstituted derivatives (130, 132). 

Butterfield, D. A., Bush, A. I. Alzheimer s amyloid beta-peptide (1-42) involvement of methionine residue 35 in the oxidative stress and neurotoxicity properties of this peptide. Neurobiol. Aging 2004, 25 563— 568. 

Pepsin (pancreative, porcine and bovine Oxidation of methionine residues Loss of enzyme properties (K13)... 

Peroxynitrite, like other oxidants, reacts with proteins, first oxidizing cysteine methionine and tryptophan residues (A7). The reaction products are sulfones, carbonyl moieties, and dityrosines (K23, M29). Formation of protein hydroperoxides and protein fragmentation was also observed (B7, G6). Nitric oxide induces oxidation of methionine residues, thus effecting oxidative damage to proteins (Cl 1). It also reacts with Fe-S clusters of aconitase (D15), though in most cases it is difficult to assess whether these effects are produced by the NO itself, or rather by a more reactive secondary product such as peroxynitrite (C5). At physiological... 

Methionine oxidation inducing abolition of protein function usually does not produce any changes in chemical and immunochemical properties of the protein. This infers that the oxidized protein can be reactivated again by reduction of sulfoxide residue, or may be catabolized through its regular proteolytic pathway. Facility of methionine oxidation, along with abundant production of various oxidants, enables oxidation of methionine residues. This rises a question concerning... 

F8. Fliss, H., Weissbach, H., and Brot, N., Oxidation of methionine residues in proteins of activated human neutrophils. Proc. Natl. Acad. Sci. USA 80, 7160-7164 (1983). 

K13. Kido, K., and Kassell, B., Oxidation of methionine residues of porcine and bovine pepsins. Biochemistry 14, 631—635 (1975). 

These derivatizations are highly selective, and may thus allow PSD measurements to be carried out on peptides after modification. Such a protocol would significantly enhance our ability to derive sequence information from PSD spectra, because the mass shifts observed in fragments help locate the particular residue within the peptide, and also confirm assignments of fragments as arising from N- or C-terminal regions. In addition to derivatizations that may modify the C- and N-termini and the derivatization of tyrosine residues, we have carried out oxidation of methionine residues with sufficient specificity to enable measurement of PSD spectra. 

Specific cleavage can be achieved by chemical or enzymatic methods. For example, cyanogen bromide (CNBr) splits polypeptide chains only on the carboxyl side of methionine residues (Figure 4.23). 

Cyanogen bromide Carboxyl side of methionine residues... 

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