S-Methylcysteine

Marks H S, Hilson J A, Leichtweis H C and Stoewsand G S (1992), S-Methylcysteine sulfoxide in Brassica vegetables and formation of methyl methanethiosulfinate from Brussels sprouts , J Agric Food Chem, 40, 2098-2101. 

S-Methylcysteine sulfoxide - precursor for 121 hemolytic factor dimethyl disulfide in cattle, but nontoxic to nonruminant animals... 

As in the case of propachlor mercapturic acid sulfoxide, the biological significance of xenobiotic mercapturic acids that contain oxidized sulfur is not known. Casida et al. (39) have reported that sulfoxidation of some thiocarbamate herbicides is a beneficial step in the detoxication process. However, cysteine conjugates can exhibit adverse biological activities. Smith (40) has reviewed work on the metabolism of the toxic principle in kale and has shown that C-S lyase action on S-methylcysteine sulfoxide produces the toxic principle. Virtanen ( ) has reviewed the processes in other plants that lead to the production of compounds with biological activity from -substituted cysteine sulfoxides. 

Iwasaki, K. (1988a) Determination of. S -methylcysteine in mouse hemoglobin following exposure to methyl bromide. Ind. Health, 26, 187-190... 

Data from several experiments with rats suggest that absorbed methyl iodide is excreted mainly in bile. Approximately 25% of an oral dose of 50 mg/kg bw was excreted in bile as 5-methylglutathione, while 2% of the same subcutaneous dose was recovered from urine and 1% of a 76 mg/kg bw oral dose was present, unchanged, in expired air within 30 min. The urinary metabolites detected in rats after subcutaneous injection, presumed to originate from. S -inethylglutathione, were. S -mcthylcysteine, A-acetyl-.S-methylcysteine, 5-methylthioacetic acid and jV-(methylthioacetyl)glycine (IARC, 1986). 

Garlic also contains S-propylcysteine-sulfoxide (PCSO) and S-methylcysteine-sulfoxide (MCSO). PCSO can generate over 50 compounds depending on temperature and water content. The action of allinase on the mixture of alliin, PCSO, and MCSO can produce many other molecules, including allyl methane thiosulfinate, methyl methanethiosulfinate, and other mixed or symmetrical thiosulfinates (R-S-S-R ), where R and R are methyl, propyl, and allyl groups. 

DMS is formed during the biodegradation of organic sulfur compounds and by the biological methylation of sulfide and methanethiol. Precursors of DMS are methionine, S-methylmethionine, dimethylsulfoniopropionate (DMSP), dimethylsulfonioacetate (DMSA), dimethyl sulfoxide (DMSO), methionine sulfoxide and sulfone, trimethylsulfonium salts, S-methylcysteine, homocysteine, dimethyl disulfide (DMDS), 2-keto-4-methiolbutyrate, and 2-mercaptoacetate (thioglycollate). 

Methionine and its S-methyl derivative, S-methylmethionine, are probably important precursors of DMS in terrestrial regions. However, plants also produce a variety of nonprotein sulfur amino adds such as S-methylcysteine, its 7-glutamyl and sulfoxide derivatives, and djenkolic add (44). The biosyntheses and functions of these compounds are poorly understood, and mechanisms for their biodegradation may be of more than academic interest, particularly with respect to the generation of volatile sulfur compounds. 

Methionine 7 -lyase Methionine Homocysteine S-methylcysteine Methionine sulfoxide Methionine sulfone S-methylmethionine (weak) Methanethiol HtS Methanethiol DMS... 

S-alkylcysteinase S-methylcysteine S-methylcysteine sulfoxide Methanethiol Methyl methane-thiosulfinate... 

Cystinuria. VII. Metabolism of S-methylcysteine, of y-thiobutyric acid, and of y-dithiobutyric acid. Ibid., 119, 689 (1937). With E. Brand and C. F. Cahill. 

S-Methylcysteine sulfoxide Allium cepa (Liliaceae) [bulb] HypoGlc, 4- cholesterol synthesis (AD rat)... 

Oxo-1 -methyl-3,4,5,6-tetrahydro-1H-1,2,4-thiadiazine-5-carboxylate 1 -oxide (364) was obtained in 87% yield from (S)-methylcysteine sulfoximine (363) with l,l -carbonyldiimidazole in the presence of DBU in dimethyl sulfoxide (84JMC228). 

Conversion of half-cystine residues in proteins and peptides to the S-methyl derivatives is advantageous in subsequent studies of amino acid sequence. Under the usual conditions of acid hydrolysis ( 2.1), S-methylcysteine is recovered in a 90% yield (Heinrikson 1971). The phenylthiohydantoin of S-methylcysteine is readily identified by routine thin layer chromatography procedures (Rochat et al. 1970). With the increasing use of the sequenator, PTH-S-methylcysteine offers a marked advantage over derivatives such as PTH-cysteic acid, or PTFl-carboxymethylcysteine, which have to be identified by special techniques (Edman 1960, 1970). S-methylcysteinyl residues provide a new point of cleavage for cyanogen bromide (5). 

Under the above conditions, the modification is totally restricted to sulfhydryl groups (Heinrikson 1971).S-methylcysteine is quantitated by amino acid analysis after acid hydrolysis ( 2.5.5). 

One example of a naturally occurring sulfoxide, available from turnips, is S-methylcysteine S-oxide (47) the CIP configuration at sulfur is (S), Draw a perspective diagram of this molecule. 

---