Identification of yolk platelet-associated hydrolases in the oocytes of Rhodnius prolixus.

The yolk platelets from Rhodnius prolixus, a blood-sucking bug, are composed mostly of vitellin and here are shown to contain at least two hydrolytic enzymes, a phosphatase and a cathepsin D-like proteinase. Both the proteinase and the phosphatase have an acid pH optimum. No hydrolytic activity was observed under alkaline or neutral conditions. Among several proteinase inhibitors tested, only pepstatin could abolish vitellin breakdown in vitro. The proteinase appears to be bound to the yolk platelet membranes. The phosphatase activity, using p-nitrophenyl phosphate as substrate, was enhanced after disruption of the platelet membrane by Triton X-100. This activity could be inhibited by tartrate but not by p-cloromercuribenzoate.