THE PORCINE SPERM MOTILITY INHIBITOR IS IDENTICAL TO BETA-MICROSEMINOPROTEIN AND IS A COMPETITIVE INHIBITOR OF NA-ATPASE(,K+)

We have isolated a small porcine seminal protein called SMI-1. Our res ults from peptide sequence, amino acid composition and mass spectral a nalyses reveal that SMI-I is identical to porcine beta-microseminoprot ein, a protein with unknown function. We also report here that this pr otein inhibits competitively the activity of Na+,K+-ATPase purified fr om porcine cerebral cortex in a dose-dependent manner. The inhibitory effect could be reversed by the addition of ATP. The half-maximal inhi bition was achieved at an inhibitor concentration of 90 mu M (C) 1996 Academic Press, Inc.