Methionine synthesis by extracts of Salmonella typhimurium

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Abstract
Following the genetic studies by Smith (1961) and Smith and Childs (1963) with methionine auxotrophs of Salmonella typhimurium, methionine formation from homocysteine has been investigated with cell-free extracts of this organism. As found with Escherichia coli (Woods, Foster and Guest, 1964), methyl groups are formed by an N5N10-methyl-enetetrahydrofolate reductase. They are then transferred to homocysteine by either a simple N5-methyltetrahydropteroyltriglutamate-honocysteine methyltransferase or alternatively a cobalamin-dependent N5-methyltetrahydrofolate-homocysteine methyltransferase; S. typhimurium differs from E. coli in being able to synthesize significant amounts of cobalamin.