Oviductin. Purification and properties of the oviductal protease that processes the molecular weight 43,000 glycoprotein of the Xenopus laevis egg envelope

The Xenopus laevis egg envelope is modified during egg transit through the pars recta oviduct. The physicochemical properties and ultrastructure of the envelope change, and the M(r) 43,000 envelope glycoprotein (gp43) is processed to M(r) 41,000. We purified a gp43 processing protease from oviductal secretory granules and studied its effects on the egg envelope. The M(r) 66,000 protease, designated oviductin, hydrolyzed the arginyl-X bond of N alpha-tert-butoxycarbonylphenylalanylserylarginyl-7-methylcoumaryl -4-amide (Km = 58 microM, kcat = 3.80 s-1). Diisopropyl fluorophosphate, EDTA, and EGTA inhibited oviductin irreversibly; soybean trypsin inhibitor, aprotinin, guanidine hydrochloride (Ki = 7.5 mM), and p-amino-benzamidine (Ki = 4.1 microM) also inhibited, but iodoacetamide, E-64, pepstatin, or 1,10-phenanthroline did not. The N-terminal amino acid sequence of oviductin was up to 64% identical to those of several serine proteases. Oviductin accounted for all of the gp43 processing activity we detected in secretory granules, and oviductin-catalyzed processing of gp43 rendered coelomic egg envelopes physically (as determined by thermal solubility) similar to those of oviposited eggs. We conclude (1) a unique serine protease secreted by the oviduct processes gp43 of the Xenopus laevis egg envelope, and (2) this processing causes physical changes in the egg envelope which occur during egg transit through the oviduct.