The binding of labelled basic proteins by boar spermatozoa.

Seminal plasma basic proteins were labelled with 131I. The efficiency of the labelling was studied by superimposing protein density traces on a radioactive fractionation plot. These labelled proteins were incubated with spermatozoa and shown to bind more readily to spermatozoa from boars after the removal of the vesicular glands than to spermatozoa obtained from their normal litter mates. Most of the labelled protein became bound to the membranes which were isolated by sucrose density gradient centrifugation. The membranes were separated into two bands which equilibrated at the relative densities of 1-150 and 1-165. These fractions consisted of membrane vesicles of different size; the smaller band on the gradient, which equilibrated at 1-165, consisted of denser membrane material.