title: 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 constant of 6 X 10(-6) s-1 at pH 7.5 and 37 degrees C and reversible conversion to an enzymically inactive stereoisomer (R configuration at sulfur) with a forward rate constant of 8 X 10(-6) s-1 at pH 7.5 and 37 degrees 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.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives; D055598:Chemical Phenomena; D002621:Chemistry; D003839:Deoxyadenosines; D004355:Drug Stability; D006714:Homoserine; D007700:Kinetics; D008968:Molecular Conformation; D012436:S-Adenosylmethionine; D013455:Sulfur; D013872:Thionucleosides
chemical_list: D003839:Deoxyadenosines; D013872:Thionucleosides; C008500:5'-methylthioadenosine; D006714:Homoserine; D013455:Sulfur; D012436:S-Adenosylmethionine; D000241:Adenosine