Gangliosides activate the phosphatase activity of the erythrocyte plasma membrane Ca 2+-ATPase

Abstract

The previous studies showed that gangliosides modulated the ATPase activity of the PMCA from porcine brain synaptosomes [Yongfang Zhao, Xiaoxuan Fan, Fuyu Yang, Xujia Zhang, Arch. Biochem. Biophys. 427 (2004) 204–212]. The effects of gangliosides on the hydrolysis of p-nitrophenyl phosphate ( pNPP) catalyzed by the erythrocyte plasma membrane Ca 2+-ATPase, which was characterized as E 2 conformer of the enzyme, were studied. The results showed that pNPPase activity was stimulated up to seven-fold, depending upon the different gangliosides used with GD1b > GM1 > GM2 > GM3 ≈ Asialo-GM1. Under the same conditions, the ATPase activity was also activated, suggesting that gangliosides should modify both E 1 and E 2 conformer of the enzyme. The Ca 2+, which drove the enzyme to E 1 conformation, inhibited the pNPPase activity, but with the similar half-maximal inhibitory concentrations (IC 50) in the presence and the absence of gangliosides. Moreover, the pNPPase activity was also inhibited by the raise in ATP concentrations. Gangliosides caused a large increase in V max, but had no effect on the apparent affinity ( K m) of the enzyme for pNPP. The kinetic analysis indicated that gangliosides could modulate the erythrocyte PMCA through stabilizing E 2 conformer.