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 E, conformer of the enzyme, were studied. The results showed that pNPPase activity was stimulated LIP to sevenfold, depending upon the different gangliosides used with GD1b > GM1 > GM2 > GM3 approximate to 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 Ca2+. which drove the enzyme to El 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 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. (c) 2005 Elsevier Inc. All rights reserved.