Fig. 1. ¹²⁵I-mZP2 and [³H]suramin bind less efficiently to proacrosin (-/-) than (+/+) mouse sperm. Binding of (A) purified ¹²⁵I-mZP2 and (B) [³H]suramin to proacrosin (+/+) and (-/-) sperm was detected by autoradiography. Micrographs (top) illustrate the typical distribution of silver grains over the sperm head. Data below show the mean number ± s.e.m. of silver grains over the head region of 100 sperm from each of nine proacrosin (-/-) and nine wild-type (+/+) mice in A, and three acrosin (-/-) and four wild-type (+/+) mice in B. Differences between (+/+) and (-/-) sperm were significant (P<0.01) in both A and B.