Enzymatic and envelope-converting activities of pars recta oviductal fluid from Xenopus laevis

Conversion of the coelomic egg envelope to the vitelline envelope of the Xenopus laevis egg is known to take place in the pars recta (PR) region of the oviduct. A method for collecting fluid generated from PR cultured in vitro was devised which enhanced the recovery of envelope-converting factors. By the criteria of melting temperature analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, ¹²⁵I labeling, ferritin binding, and in vitro fertilization assays, the secretions collected from PR cultured in vitro were capable of modifying the envelope in a manner analogous to that which occurred in vivo, including the limited hydrolysis of one envelope glycoprotein. Hydrolytic activities present in PR fluid were assayed with a number of peptide and carbohydrate substrates. Enzymes which hydrolyzed t-butyloxycarbonyl-Leu-Ser-Thr-Arg-methylcouma t-butyloxycarbonyl-Phe-Ser-Arg-methylcoumarylamide, and t-butyloxycarbonyl-Val-Leu-Lys-methylcoumarylamide were found to be present in PR fluid at levels elevated by threefold or more over amounts found in a comparable volume of blood plasma.