Soybeans and radish leaves contain only one of the sulfonium diastereoisomers of S-adenosylmethionine

Abstract

Using a liquid chromatography method that separates the two sulfonium diastereoisomers of adenosylmethionine, we have found that immature soybeans, soybean callus culture, radish leaves, yeast and rat liver contain only the ( S)-sulfonium form of S-adenosylmethionine. Our findings contradict the suggestion by Stolowitz and Minch that 10–20% of naturally-occurring adenosylmethionine may have the ( R)-configuration at the sulfonium pole. Absence of the ( R)-sulfonium isomer of adenosylmethionine in biological materials indicates that the ( R)-sulfonium form of adenosylmethionine present in commercial adenosylmethionine samples is an artifact of the isolation procedure. Our method of measuring the isomers of adenosylmethionine enabled us to readily determine the rate of racemization and hydrolysis of adenosylmethionine. Our rate constants for racemization ( K r ) and hydrolysis ( K h ) were 2.4 × 10 −6 sec −1 and 12.3 × 10- −6 sec −1, respectively; values which are noticeably different from those of Wu and co-workers which were obtained with a more complicated method ( K r = 8 × 10 −1 sec −1; K h = 6 × 10 −6 sec −1). We believe the absence of the ( R)-isomer in vivo is best explained by stabilization of the ( S)-isomer as suggested by Wu et al. Although the tissues we have analysed contained the ( S)-sulfonium form of adenosylmethionine exclusively, when ethionine-resistant soybean cell lines were given ethionine, they accumulated both sulfonium diastereoisomers of adenosylethionine.