CHARACTERIZATION OF THE F1F0-ATPASE AND THE TIGHTLY-BOUND ATPASE ACTIVITIES IN SUBMITOCHONDRIAL PARTICLES FROM HUMAN TERM PLACENTA

In a previous study we demonstrated the existence of a tightly-bound A TPase in the human placental mitochondria (Martinez et al., 1993). The current study characterizes the ATP hydrolysis produced by the F1F0-A TPase and the tightly-bound ATPase in submitochondrial particles from the human term placenta. Both enzymes were not differentiated by pH. I nhibitors were necessary to distinguish the activity of each enzyme. T he kinetic of the total ATP hydrolysis fitted into a model of two enzy mes. During the characterization, it was observed that the tightly-bou nd ATPase activity was partially inhibited by vanadate and Mg2+ , wher eas the F1F0-ATPase was totally inhibited by Mg2+. Different nucleotid es were hydrolyzed by the tightly-bound ATPase; the F1F0-ATPase hydrol yzed exclusively ATP. Glucose-6-phosphate, p-nitrophenylphosphate, or pyrophosphate were not hydrolyzed by the F1F0-ATPase, although some hy drolysis was observed with the tightly-bound ATPase. It is concluded t hat the tightly-bound ATPase activity corresponded to a 5'-nucelotidas e, and that the human placental mitochondria could participate in the metabolism of nucleotides. (C) 1996 W. B. Saunders Company Ltd