Enzymic synthesis of spermine in rat prostate

The enzymic synthesis of spermine by soluble preparations from rat ventral prostate was demonstrated. Spermine was formed from spermidine and either S-adenosyl-l-methionine or "decarboxylated S-adenosyl-l-methionine" (the latter prepared with the aid of a bacterial enzyme). Partial purification of the enzyme system responsible for spermidine synthesis led to isolation of the spermine-forming system in the same yield. The two activities could not be distinguished on the basis of thermal stability, and it is possible that a single prostatic enzyme catalyzes the production of both spermidine and spermine. At saturating levels of all reactants, the maximal rate of spermine synthesis by the most purified preparations was only about 25% of the rate of spermidine formation. The affinities of various substrates for the spermine-synthesizing enzyme system were determined. Putrescine was found to be a competitive inhibitor of spermine synthesis. S-Adenosyl-l-ethionine was, in comparison with S-adenosyl-l-methionine, only weakly active as a precursor of spermine. The relationship of these findings to the biosynthesis of spermine by the prostate gland in vivo is discussed.