Comparative studies of Bufo and Xenopus vitelline coat molecular transformations induced by homologous and heterologous oviducal pars recta proteases

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Abstract
The vitelline coats (VCs) of Bufo japonicus and Xenopus laevis undergo coelomic egg (CEVC)‐ to uterine egg (UEVC)‐type conversions, after passage through the pars recta (PR) portion of oviduct or treatment of eggs with secretory granules from PR (PRGs), as determined by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) analyses of glycoproteins. These conversions include for Bufo the loss of 40K–52K components from the CEVC, concomitant with increasing stainability of a 39K component and the appearance of a 36K component in the UEVC. For Xenopus, a 43K glycoprotein in the CEVC is transformed to a 41K glycoprotein in the UEVC. When coelomic eggs of both Bufo and Xenopus were treated with PRGs from the heterologous species, the macromolecular components of the VCs were processed in exactly the same way as with homologous PRGs. The PRGs from both species showed strikingly similar hydrolytic activities against Boc‐Val‐Leu‐Lys‐MCA and several peptidyl‐Arg‐MCAs. Bufo coelomic eggs treated with Xenopus PRGs were not fertilizable by Bufo sperm, whereas treatment with Bufo PRGs rendered the eggs fertilizable. We conclude that the oviductal enzymes and VC substrates in these species are evolutionarily conserved and that macromolecular alterations of VC glycoproteins as detected by SDS‐PAGE are necessary, but not sufficient, for making coelomic eggs fertilizable.

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