S-Adenosylmethionine decarboxylase was purified to homogeneity from rat liver and from rat psoas. The major step involved affinity chromatography on methylglyoxal bis- (guanylhydrazone) linked to Sepharose. The muscle enzyme was more tightly retained to this absorbent, and the enzymes from the two sources could readily be separated by chromatography on this material. The psoas and liver enzymes could not be distinguished by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, both giving a single band corresponding to an Mr of 32 500, but were separated by electrophoresis under nondenaturating conditions and by isoelectric focusing (the isoelectric points were 5.3 for psoas and 5.7 for liver enzyme). The liver and psoas enzymes also differed in respect to Km for S-adenosylmethionine, the degree to which they were activated by putrescine, and their sensitivity to inhibition by methylglyoxal bis(guanylhydrazone) and related compounds. These results indicate that there are two forms of S-adenosylmethionine decarboxylase. The presence of a particular form could, therefore, be important both in the regulation of polyamine levels and also in the pharmacology involving inhibitors of polyamine synthesis.
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