The synthesis of methionine from homocysteine by enzymic extracts of Escherichia coli

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Abstract
Soluble extracts of acetone-dried Escherichia coli (an auxotrophic strain requiring serine or glycine for growth) synthesize methionine from homocysteine and serine. After dialysis of the enzyme extract there are requirements (not absolute) for phosphate and magnesium ions, adenosine triphosphate, diphosphopyridine nucleotide and a heated extract of E. coli. The heated extract of E. coli probably contains a coenzyme form of folic acid. It is not replaced by tetrahydroptero-ylglutamic acid or its N5-formyl derivative. It is partially replaced by a N-formylpteroyltriglutamic acid extracted from Clostridium cylindrosporum. Isotope technique showed that the [beta]-carbon atom of serine became the methyl-carbon atom of methionine. The enzymic extracts also degraded serine to glycine; the cofactor requirements were qualitatively similar to those for methionine synthesis.