KINETICS OF CALCIUM-TRANSPORT THROUGH PURIFIED PLASMA-MEMBRANE OF BUFFALO (BUBALUS-BUBALIS) SPERMATOZOA - EFFECT OF CALMODULIN-LIKE PROTEIN

A procedure is described for the isolation, identification, and purifi cation of plasma membrane from buffalo ejaculated spermatozoa. A typic al yield of plasma membrane vesicles obtained by this procedure was 28 0 mu g of membrane protein per 10(9) spermatozoa. Kinetics of calcium transport through purified plasma membrane vesicles were studied using Ca-45(2+). The transport of Ca2+ through plasma membrane vesicles was electrogenic with maximum Ca2+ uptake (47 mu mol) occurring at 30 min in the presence of 0.25 mM ATP. K-m and V-max values for Ca2+ transpo rt were 0.25 mM and 182 mu mol, respectively, whereas in the presence of variable concentrations of free Ca2+, the K-m and V-max values were 0.23 mu mol and 82.3 mu mol, respectively. Calmodulin-like protein (2 0 mu g) significantly (p < 0.01) inhibited the Ca2+ accumulation in th e plasma membrane vesicles. It is demonstrated that calmodulin-like pr otein regulates Ca2+ transport during sperm capacitation and acrosome reaction.