S-Methylmethionine is a derivative of methionine with the chemical formula2S+CH2CH2CHCO2−. This cation is a naturally-occurring intermediate in many biosynthetic pathways owing to the sulfoniumfunctional group. It is biosynthesized from L-methionine which is first converted to S-adenosylmethionine. The subsequent conversion, involving replacement of the adenosyl group by a methyl group is catalyzed by the enzyme methionine S-methyltransferase. S-methylmethionine is particularly abundant in plants, being more abundant than methionine. S-Methylmethionine is sometimes referred to as vitamin U, but it is not considered a true vitamin. The term was coined in 1950 by Garnett Cheney for uncharacterized anti-ulcerogenic factors in rawcabbage juice that may help speedhealing of peptic ulcers.
Biosynthesis and biochemical function
S-Methylmethionine arises via the methylation of methionine by S-adenosyl methionine. The coproduct is S-adenosyl homocysteine. The biological roles of S-methylmethionine are not well understood. Speculated roles include methionine storage, use as a methyl donor, regulation of SAM. A few plants use S-methylmethionine as a precursor to the osmolytedimethylsulfoniopropionate. Intermediates include dimethylsulfoniumpropylamine and dimethylsulfoniumpropionaldehyde. S-Methylmethionine is claimed to have protective effects in the gastrointestinalmucosa and in the liver.
S-Methylmethionine is found in barley and is further created during the malting process. SMM can be subsequently converted to DMS during the malt kilning process. Lightly kilned malts such as pilsner or lager malts retain much of their SMM content while higher kilned malt such as pale ale malt has substantially more of the SMM converted to DMS in the malt. Darker kilned malts such as Munich malt have virtually no SMM content since most has been converted to DMS. Other crystal malts and roasted malts have no SMM content and often no DMS content since the kilning also drives that compound out of the malt.
