Characterization of cell surface polypeptides of unfertilized, fertilized, and protease‐treated zona‐free mouse eggs

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Abstract
The polypeptide composition of unfertilized, fertilized, and protease‐treated zona‐free mouse eggs was evaluated in this study. Zona‐free eggs were radioiodinated by an Iodogen‐catalyzed reaction. Light microscopic autoradiography of egg sections revealed that labeling was restricted to the cell surface. Labeled eggs were solubilized, and cell surface polypeptides were identified by one‐dimensional SDS polyacrylamide gel electro‐phoresis and autoradiography. The unfertilized egg demonstrated 8–10 peptides that incorporated125I, with major bands observed at approximately 145–150, 94, and 23 kilo‐daltons (kD). Zona‐free eggs fertilized in vitro and then radiolabeled demonstrated several new bands in comparison to unfertilized eggs, with a major band appearing at approxi mately 36 kD. Treatment of radiolabeled unfertilized eggs with either trypsin or chymo‐trypsin (1 mg/ml for 5–20 min) caused enzyme‐specific modifications in labeled polypep tides. Trypsin (T) treatment resulted in time‐dependant modification of the three major peptides at 145–150,94, and 23 kD. Chymotrypsin (CT) treatment, in contrast, was asso ciated with loss or modification of the 94 kD band, with no apparent effect on either the 145–150 or 23 kD band. Taken together with previous data indicating that T or CT egg treatment interferes with sperm‐egg attachment and fusion (Boldt et al.: Biol Reprod 39:19–27, 1988), these results suggest a possible role for the 94 kD protein in sperm‐egg interaction.