Gangliosides activate the phosphatase activity of the erythrocyte plasma membrane Ca2+-ATPase

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 Ca2+-ATPase, which was characterized as E2 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 E1 and E2 conformer of the enzyme. The Ca2+, which drove the enzyme to E1 conformation, inhibited the pNPPase activity, but with the similar half-maximal inhibitory concentrations (IC50) 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 Vmax, but had no effect on the apparent affinity (Km) of the enzyme for pNPP. The kinetic analysis indicated that gangliosides could modulate the erythrocyte PMCA through stabilizing E2 conformer.