EFFECT OF TYROSINASE PREPARATIONS ON OXYTOCIN, VASOPRESSIN AND BRADYKININ

Abstract

On incubation with a tyrosinase preparation at p H 7.5, oxytocin and vasopressin were inactivated. The loss of oxytocic activity did not differ significantly from that of milk‐ejecting activity in oxytocin, nor the loss of pressor activity from that of antidiuretic activity in vasopressin. Oxytocin was inactivated less rapidly at p H 6.6 than at p H 7.5. At p H 3.9 neither oxytocin nor vasopressin was inactivated. Analogues of oxytocin and vasopressin, in which tyrosine is replaced by phenylalanine, were not inactivated by the tyrosinase preparation used. On incubation of bradykinin with two different tyrosinase preparations, there was no loss of oxytocic activity at p H 7.5 but an almost total loss at p H 3.9. In the presence of p‐nitrophenol, ascorbic acid, sodium diethyldithiocarbamate and during incubation under anaerobic conditions the inactivation of oxytocin at p H 7.5 was inhibited, but not that of bradykinin at p H 3.9. It is concluded that the tyrosinase preparations used contain two distinct enzymes or activities, the one inactivating oxytocin and vasopressin at p H 7.5 and the other bradykinin at p H 3.9.