Chiral instability at sulfur of S-adenosylmethionine

Abstract
S-Adenosylmethionine, generated enzymically in chirally pure form (S configuration at sulfur), undergoes simultaneous irreversible conversion to 5''-deoxy-5''-(methylthio)adenosine and homoserine with a rate constnat of 6 .times. 10-6 s-1 at pH 7.5 and 37.degree. C and reversible conversion to an enzymically inactive stereoisomer (R configuration at sulfur) with a forward rate constant of 8 .times. 10-6 s-1 at pH 7.5 and 37.degree. C. These forms of instability require small turnover times and/or stabilization through macromolecular binding for S-adenosylmethionine, if organisms that utilize it are to avoid losses of metabolic energy.