On the role of S-adenosyl-L-methionine in the biosynthesis of spermidine by rat prostate.

The isolation from the rat ventral prostate of a soluble enzyme preparation producing spermidine, COZ, and methylthioadenosine from putrescine and S-adenosyl-L-methionine is described. This preparation catalyzes limited decarboxylation of S-adenosyhnethionine in the absence of any additional reactants but maximal rates of CO2 release from S-adenosyhnethionine require the presence of putrescine. When putrescine is present, spermidine and methylthioadenosine are produced in amounts stoichiometric with the CO2 released. The decarboxylation of S-adenosyhnethionine in the presence of putrescine is inhibited by isonicotinic acid hydrazide and by 4-bromo-3-hydroxybenzyloxyamine. This tiding suggests that pyridoxal phosphate is a cofactor of the reaction. The prostatic enzyme preparation also catalyzes the formation of spermidine from putrescine and exogenous decarboxylated S-adenosyhnethionine (prepared by the action of Escherichia coli S-adenosyhnethionine decarboxylase). The affinities for S-adenosyhnethionine, decarboxylated S-adenosyhnethionine, and putrescine were measured. The prostatic preparation could not be separated into two enzymic fractions, one catalyzing the decarboxylation of S-adenosyhnethionine, and the other catalyzing spermidine synthesis, as is the case with the spermidine-synthesizing system of E. coli. The differences between the prostatic and the bacterial spermidine-synthesizing systems are discussed. Spermine is synthesized by the preparation from the rat ventral prostate in the presence of S-adenosylmethionine and spermidine, but at a considerably slower rate than spermidine synthesis from putrescine and Sadenosylmethionine.