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Abstract

Outer cytoplasmic membranes of Xenopus laevis eggs were isolated by manual dissection. Cortices of unfertilized eggs and membranes of fertilized stages were subjected to SDS-polyacrylamide gel electrophoresis. The Coomassie-blue stained gels of membranes from unfertilized eggs and fertilized stages showed 21 and 17 major bands, respectively, covering a molecular weight range of 27000–275000 Daltons. To demonstrate their purity, the preparations were examined by light and electron microscopy and the gel patterns were compared with those of gel electropherograms of isolated envelopes, yolk and pigment granules.

To detect membrane proteins that reside in the outer membrane surface, the eggs were exposed to ¹³¹Iodine in the presence of lactoperoxidase. Approximately four proteins of molecular weights of 115000, 78000, 55000 and 27000 Daltons were labelled. In addition, all except one of the proteins of the vitelline envelope were strongly labelled, while the yolk platelets could only be iodinated after isolation.

Changes of cortical protein patterns were studied in eggs and cortices: a) after fertilization; b) after activation by calcium-ionophore A 23187; c) after addition of calcium and distilled water to isolated cortices; and d) after incubation in the presence of the proteolytic enzyme papain. After fertilization, bands with molecular weights of 246000, 181000, 166000 and 34000 Daltons were missing. Ionophore and calcium treatment of unfertilized eggs produced a protein pattern similar to that observed after normal fertilization. After papain treatment, the band patterns of the membranes were not significantly different from those of cortices of unfertilized eggs.