Effect of Adenosylethionine on 5-Methyltetra-hydrofolate-homocysteine Transmethylase

Abstract

THE 5 - methyltetrahydrofolate - homocysteine transmethylase of Escherichia coli requires catalytic quantities of S-adenosyl-L-methionine¹ and a vitamin B₁₂ derivative for activity². It was of interest to determine the effect of S-adenosyl-L-ethionine on this reaction since this compound can substitute for adenosylmethionine in certain enzyme-catalysed reactions such as the formation of the ethyl derivatives of phospholipid choline, creatine, histidine and carnosine^3,4. Adenosylethionine bromide was isolated from rat liver after ethionine feeding⁵. It behaved as a single spot on a paper chromatogram with 1-butanol–acetic acid–water (60:15:25, v/v/v) as the solvent. After boiling in 0.1 N sodium hydroxide for 1 h a chromatogram of the digest yielded spots for ethionine, homo-serine and adenine⁵. Adenosylmethionine iodide was purchased from Calbiochem, Los Angeles, Calif. It was found (Table 1) that adenosylethionine could not replace adenosylmethionine in the reaction under investigation. When added simultaneously at equal concentration little or no effect was observed. Significant inhibition was observed when adenosylethionine was pre-incubated with the enzyme or when higher concentrations of adenosylethionine were employed.