Mechanisms and regulation of polyamine and putrescine biosynthesis in male genital glands and other tissues of mammals

The experimental results presented in this paper are largely concerned with enzymes involved in the biosynthesis of putrescine, spermidine, and spermine in the rat ventral prostate gland. The occurrence and possible functions of polyamines in male accessory genital glands and their secretions are first reviewed. Evidence is presented that the decarboxylation of l-ornithine by a specific soluble, pyridoxal phosphate-dependent enzyme is the principal pathway for the biosynthesis of putrescine in the prostate. Biochemical reactions involved in the formation and utilization of l-ornithine in this gland are discussed in relation to the provision of this amino acid for polyamine synthesis. Spermidine is synthesized in the ventral prostate by a soluble, putrescine-activated S-adenosylmethionine decarboxylase system which forms CO₂, spermidine, and thiomethyladenosine in stoichiometric amounts. This enzyme system has been partially purified, and many of its properties are described. Although decarboxylated S-adenosylmethionine (prepared with an enzyme from E. coli) serves well as a propylamine donor for spermidine synthesis by the prostatic enzyme system, the latter could not be fractionated into a distinct S-adenosylmethionine decarboxylase and a separate "propylamine transferase" as previously described in micro-organisms by C. W. Tabor. It is proposed that spermidine synthesis in the prostate gland may not involve free decarboxylated S-adenosylmethionine as an intermediate. Spermine synthesis from spermidine and S-adenosyl-methionine (or its decarboxylated derivative) was demonstrated with soluble prostatic extracts; the mechanism(s) of spermine biosynthesis are discussed. Enzymes degrading putrescine, spermidine, and spermine could not be demonstrated in rat ventral prostate. Large and rapid increases in the activity of both ornithine decarboxylase and the putrescine-dependent S-adenosylmethionine decarboxylating system occur during the early phases of prostatic growth induced by testosterone in orchiectomized rats. The role of polyamines in the androgen-dependent functional differentiation of the prostate is considered.