Polyamines and transglutaminase actions

Polyamines (putrescine, spermidine and spermine), secreted by the prostate gland, occur in high concentrations in the seminal fluid of many species, including man and rat. The physiological significance of seminal polyamines is still obscure, however. It has been postulated that polyamines may serve as amine donor substrates for transglutaminases (TGases), enzymes catalyzing protein crosslinking by the formation of gamma-glutamyl-lysine or bis(gamma-glutamyl)polyamine cross-bridges. We have analyzed TGase-activities and polyamine content of the various rat prostate lobes and rat seminal vesicles. Highest TGase activities were observed in the coagulating gland (anterior prostate) and the dorsolateral prostate, whereas very little TGase activity was present in the ventral prostate gland. In contrast, polyamine concentrations were highest in the ventral prostate but low in coagulating glands. Seminal vesicles, and in particular seminal vesicle secretions, contained low polyamine levels and intermediate TGase activity. Levels of protein-bound polyamines, not extractable by perchlorid acid, did not correlate with TGase-activities in ventral prostate and coagulating glands, suggesting an extracellular rather than intracellular function of prostatic TGase and polyamines. The observation that Km-values of rat prostate TGase for all three polyamines (57-120 microM, using N,N-dimethylated casein as protein substrate) were well below seminal polyamine concentrations is compatible with a regulatory role of polyamines in the process of seminal clot formation.