SOYBEANS AND RADISH LEAVES CONTAIN ONLY ONE OF THE SULFONIUM DIASTEREOISOMERS OF S-ADENOSYLMETHIONINE

Using a liquid chromatography method that separates the 2 sulfonium diastereoisomers of adenosylmethionine, it was found that immature soybeans, soybean callus culture, radish leaves, yeast and rat liver contain only the (S)-sulfonium form of S-adenosylmethionine. These 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. The method used for measuring the isomers of adenosylmethionine permitted determination of the rate of racemization and hydrolysis of adenosylmethionine. The rate constants for racemization (Kr) and hydrolysis (Kh) were 2.4 .times. 10-6 s-1 and 12.3 .times. 10-6 s-1, respectively; values which are noticeably different from those of Wu and coworkers which were obtained with a more complicated method (Kr = 8 .times. 10-6 s-1; kh = 6 .times. 10-6 s-1). 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 tissue analyzed contained the (S)-sulfonium form of adenosylmethionine exclusively, when ethionine-resistant soybean cell lines were given ethionine, they accumulated both solfonium diastereoisomers of adenosylethionine.