Regulation of ATP-dependent Ca-uptake of synaptic plasma membranes by Ca-dependent modulator protein

Abstract

1. 1)Treatment of synaptic plasma membranes (S.P.M.) with 1 mM EGTA decreased their MgCaATPase activity about 50% without significantly affecting their MgATPase or NaKATPase activity. 2. 2)EGTA-treatment of S.P.M. did not affect the maximum binding of Cd-uptake but decreased its initial velocity about 50%. This treatment also decreased Ca-accumulation in the presence of oxalate about 60%. 3. 3)Addition of Ca-dependent modulator protein (M.P.) purified from bovine brain to EGTA-treated S.P.M. completely restored that MgCaATPase activity and Ca-uptake to the control levels and partially restored their Ca-accumulation. The half-maximum activations of MgCaATPase, Ca-uptake and Ca-accumulation were observed with about 3 μg of M.P. per mg protein of S.P.M. These results suggest that M.P. regulates MgCaATPase and the translocation of Ca ion at the S.P.M.