Decarboxylated S-adenosylmethionine in mammalian cells

The content of decarboxylated S-adenosylmethionine in rat tissues was found to be of the order of 0.9 to 2.5 nmol/g wet weight, about 2 to 4% of the content of S-adenosylmethionine. Three methods were used for determinations: separation by high pressure liquid chromatography followed by quantitation using UV absorbance, separation by paper electrophoresis after labeling with radioactive methionine to get the ratio of S-adenosylmethionine to decarboxylated S-adenosylmethionine, and separation by electrophoresis followed by elution and assay by an isotope dilution technique using spermidine synthase. The three methods gave comparable results, although the labeling with methionine appeared to slightly overestimate levels in the liver. Hepatic decarboxylated S-adenosylmethionine content was reduced by more than 90% for at least 8 h by treatment with methylglyoxal bis(guanylhydrazone), a potent reversible inhibitor of S-adenosylmethionine decarboxylase, but had returned to control levels by 24 h. The related irreversible inhibitor, 1,1'-[(methylethanediylidene)-dinitrilo]bis(3-aminoguanidine), reduced levels slightly less to about 20% of control, but maintained them at this value for 2 days.