Distribution of Pz-peptidase in bovine epididymal and ejaculated semen

Bovine epididymal or ejaculated semen was fractionated by density gradient centrifugation in Percoll, and seminal components recovered from the gradients were subjected to additional separation and washing steps. This procedure resulted in isolation of four major seminal constituents: particle-free extracellular fluid, washed light particulates, washed cytoplasmic droplets, and washed spermatozoa. When assayed using the Pz-peptide substrate, all the isolated seminal fractions contained substantial Pz-peptidase activity. The extracellular fluid Pz-peptidase was present in soluble form, but Triton X-100 was required for complete extraction of the Pz-peptidase activity from the spermatozoa, cytoplasmic droplets, and light particulates. The greatest Pz-peptidase activities were observed in the cytoplasmic droplet and epididymal sperm extracts, whereas the activities in extracellular fluid, extracts of light particulates, and extracts of ejaculated spermatozoa were relatively low. Most of the Pz-peptidase activity in extracts of epididymal spermatozoa was attributable to cytoplasmic droplets. The specific Pz-peptidase activities found by regression analysis were 6.1 mU/billion attached cytoplasmic droplets and 1.1 mU/billion spermatozoa. These results established that in the bovine, cytoplasmic droplets were the major source of Pz-peptidase activity in semen and that Pz-peptidase was not primarily a spermatozoal enzyme.