Methionine sulfone, formation

Furthermore, it should be mentioned that some of the amino acid side-chain modifications are actually reversible, including thiolation and disulfide bond formation, whereas others are irreversible, like methionine sulfone formation or nitration. 

Methionine sulfoxide formation may occur without noticeable changes in physical or immunochemical properties of the protein. Thus reduction of sulfoxide to thioether often completely restores the lost protein function. Many cells, including human polymoprhonuclear neutrophilic leukocytes, contain enzyme methionine sulfoxide reductase, which is able to convert methionine sulfoxide to the reduced methione form in a variety of proteins (B25, F8). Methionine reacting with a strong oxidant effects methionine sulfone production, which in vivo is not reduced back to methionine. 

After oxidation of unmodified proteins with performic acid ( 3.8.1) the methionine will all be present as methionine sulfone, and the cysteine and cystine will be present as cysteic acid. The method for oxidizing proteins with performic acid on a preparative scale ( 3.8.1) has been modified for analytical studies (Moore 1963), to allow rapid destruction of excess performic acid. However, tryptophan is still destroyed by the performic acid in this modified procedure, and quantitation of tyrosine may be complicated by the formation of halogenated derivatives ( 2.2.3). 

Fig. 3A, B Protein repair mechanisms. Panel A demonstrates the oxidation of thiol groups, leading to the formation of an intermolecular cross-link. This modification can be repaired by two mechanisms, one involving gluathione and the other thioredoxin. Panel B demonstrates the methionine oxidation,leading to methionine sulfoxide and methionine sulfone. Methionine sulfoxide can be repaired either in its protein-bound or soluble form by two types of enzymes (1 and 11). For more detailed description see the text...

The alkaline Fe(CN)6 oxidations, described hereafter, were found to be first order in Fe(CN)g ion. The oxidation of DL-methionine (Meth) was fractional order both in Meth and OH ions. The mechanism assumed the formation of an adduct, of Fe(CN)6 and Meth, which decomposed to a radical in the rate-determining step. Further oxidation of the radical in the fast step resulted in the product methionine sulfoxide. The same reaction catalysed by Ru(III) was first order in Ru(III), had a fractional order in OH , and slowed with increasing methionine concentrations. The proposed mechanism suggested the formation of a complex between [Ru(H20)50H] +, the reactive Ru(III) species, and Meth. The product was methionine sulfone nitrile. The outer-sphere Ru(III)-catalysed oxidation of L-proline to glutamic acid was first order in Ru(III), fractional order in OH , and of zero order in proline.The oxidation of serine and threonine was first order in amino acid and zero order in OH . The reactivities of serine and threonine... 

A number of Ir(lll)-, Ru(lll)- and Os(VIII)-catalysed redox studies of organic compounds by alkaline hcf are reported. The rates of Ir(III)-catalysed oxidations of arginine and lysine show Michaelis-Menten dependence in amino acids and increase with ionic strength the proposed mechanism assumes the formation of an lr(IIl)-amino acid complex. This study was also published by the authors in another journal. The Ir(in)-catalysed alkaline oxidation of OL-methionine (met) by hcf to methionine sulfone is fractional order in met. The reaction rates increase with increase in OH coneentration. The active species of oxidant and catalyst are [FeCCN) ] and [IrClgCHjOljOH]", respectively. The results of the uncatalysed oxidation of DL-methionine (met) are similar to those of the catalysed reaction. 

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). 

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... 

Peptide lynlhesh. The unwanted side reactions often encountered in the synthesis of peptides containing methionine cun be eliminated by the temporary conversion of the Ihioether function of methionine into the sulfoxide at any stage of a peptide lyntheils. The lulfoxlda oxygen is Introduced wlthoui formation of the sulfone when... 

Fig. 1 Posttranslational redox modificatitnis to amino acids in proteins. Many amino acids can undergo various posttranslatiraial redox modifications in the presence of NAPQI, oxidative stress, and nitrosative stress. Thiols in cysteine can undergo covalent binding, mixed disulfide formation, nitrosylation, and become oxidized to sulfenic, sulfinic, and sulfonic acids. Tyrosine can become nitrated by peroxynitrate, and methionine can be oxidized by ROS to methionine sulfoxide. Not shown are many other oxidatirais that can occur to other amino acids such as proline, histidine, etc.

Studies conducted in rabbit liver microsomes on the metabolism of methyl, ethyl, isopropyl and propyl thiols show that rabbit liver catalyses the S-methylation of short-chain alkane thiols to yield the corresponding methyl sulfides. The coenzyme in this process is S-adenosyl-L-methionine. The resulting methyl sulfides are further metabolized by formation of the corresponding sulfoxide and sulfone (Holloway et al., 1979). The methylation of short-chain alkyl thiols to methylthioethers acts as a detoxication mechanism for the reactive sulfhydryl group (Holloway et al., 1979),... 

There is formation of the corresponding sulfoxyde. In some other conditions, the reaction limit may also be the corresponding sulfone. We may admit that methionine is the reduced form of the couple... 

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