Methionine, sulfide oxidation

HOCl-mediated protein oxidation accelerates under pathophysiological conditions. Thus, proteins from extracellular matrix obtained from advanced human atherosclerotic lesions contained the enhanced levels of oxidized amino acids (DOPA and dityrosine) compared to healthy arterial tissue [44], It was also found that superoxide enhanced the prooxidant effect of hypochlorite in protein oxidation supposedly by the decomposition of chloramines and chlor-amides forming nitrogen-centered free radicals and increasing protein fragmentation [45], In addition to chlorination, hypochlorite is able to oxidize proteins. The most readily oxidized amino acid residue of protein is methionine. Methionine is reversibly oxidized by many oxidants including hypochlorite to methionine sulfide and irreversibly to methionine sulfone [46] ... 

In general, sulfide radical cations would either deprotonate in the a-position to the sulfur, yielding a-(alkylthio)alkyl radicals, or engage in the one-electron oxidation of additional substrates. However, recent hypothesis and results have focused on a possible role of methionine sulfide radical cations in hydrogen abstraction reactions within the Alzheimer s disease yS-amyloid peptide (ySAP) [73]. These mechanisms will be discussed here in some detail. 

Sulfur-containing amino acids, such as methionine and cystine, are probably the precursors of the mercaptans, sulfides, and disulfides.3 Dimethyl sulfide yields dimethyl sulfoxide and its oxidized product dimethyl... 

Peroxynitrite easily oxidizes nonprotein and protein thiyl groups. In 1991, Radi et al. [102] have shown that peroxynitrite efficiently oxidizes cysteine to its disulfide form and bovine serum albumin (BSA) to some derivative of sulfenic acid supposedly via the decomposition to nitric dioxide and hydroxyl radicals. Pryor et al. [124] suggested that the oxidation of methionine and its analog 2-keto-4-thiomethylbutanic acid occurred by two competing mechanisms, namely, the second-order reaction of sulfide formation and the one-electron... 

SULFUR (In Biological Systems). Sulfur, in some form, is required by all living organisms. It is utilized in various oxidation stales, including sulfide, elemental sulfur, sulfite, sulfate, and thiosulfate by lower forms and in organic combinations by all. The more important sulfur-containing organic compounds include the amino acids (cysteine, cystine, and methionine, which are components of proteins) the vitamins thiamine and... 

Sulfate and Organic Sulfates. Inorganic sulfate ion (SO L-) occurs widely in nature. Thus, it is not surprising that this ion can be used in a number of ways in biological systems. These uses can be divided primarily into two categories (1) formation of sulfate esters and the reduction of sulfate to a form that will serve as a precursor of the amino acids cysteine and methionine and (2) certain specialized bacteria use sulfate to oxidize carbon compounds and thus reduce sulfate to sulfide, while other specialized bacterial species derive energy from the oxidation of inorganic sullur compounds to sulfate. 

Figure l. Microbial transformations of methionine which generate methylated sulfides. 1) methionine 7-lyase 2) and 3) possible demethiolations 4) chemical and probably biochemical oxidation 5) thiol S-methyltransferase. 

Sulfur Compounds of Beef Flavor. Methional, which results from the degradation of methionine, is an important contributor to flavor in meat. Thiolanes, formed during the cooking of beef, have peculiar oniony flavors that also augment the quality of the meaty flavor. Thiophenes and thiofurans are also important to meaty flavors. Sulfides, such as methyl sulfide, are oxidized to methyl sulfoxide and methyl sulfone. Condensation reactions of Maillard browning products also result in thiazoles such as benzothiazole, an important component of meat flavor. 

There has been no report on the spectrum of methionine sulfone, which is found in hydrolyzates of performate-oxidized proteins. It will probably be not very different from cysteic acid at wavelengths > 2000 A, since simple sulfones are generally transparent to 1800 A (Koch, 1950). Methionine sulfoxide is a stable amino acid found in human urine, in a variety of plant tissues, and as an intermediate in the oxidation of methionine to the sulfone. Its absorption spectrum has not been recorded. The sulfoxide chromophore is usually a broad band, located around 2100 A and of about the same intensity as alkyl sulfides (Koch, 1950). An interesting... 

Bobrowski K, Hug GL, Pogock D, Marciniak B, Schoneich C. (2007) Stabilization of sulfide radical cations through complexation with the peptide bond Mechanisms relevant to oxidation of proteins containing multiple methionine residues. J Phys Chem Sill 9608-9620. 

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