Presence of two enzymes, different from the F1F0-ATPase, hydrolyzing nucleotides in human term placental mitochondria

The hydrolysis of ATP, ADP or CTP was characterized in mitochondria and sub mitochondrial particles since a tightly-bound ATPase associated with the in ner mitochondrial membrane from the human placenta has been described, Subm itochondrial particles, which are basically inner membranes, were used to d efine the location of this enzyme. Mitochondria treated with trypsin and sp ecific inhibitors were also used, The oxygen consumption stimulated by ATP or ADP was 100% inhibited in intact mitochondria by low concentrations of o ligomycin (0.5 mu g/mg) or venturicidine (0.1 mu g/mg), while the hydrolysi s of ATP or ADP was insensitive to higher concentrations of these inhibitor s but it was inhibited by vanudate. Oligomycin or venturicidine showed a di fferent inhibition pattern in intact mitochondria in relation to the hydrol ysis of ATP, ADP or GTP. When suhmitochondrial particles were isolated from mitochondria incubated with oligomycin or venturicidine, no further inhibi tion of the nucleotide hydrolysis was observed. contrasting with the partia l inhibition observed in the control, By incubating the placental mitochond ria with trypsin, a large fraction of the hydrolysis of nucleotides was eli minated. In submitochondrial particles obtained tl-om mitochondria treated with trypsin or trypsin plus oligomycin, the hydrolysis of ATP was 100% sen sitive to oligomycin at low concentrations, resembling the oxygen consumpti on; however, this preparation still showed some ADP hydrolysis. Native gel electrophoresis showed two bands hydrolyzing ADP, suggesting at least two e nzymes involved in the hydrolysis of nucleotides. besides the F1F0-ATPase. It is concluded that human placental mitochondria possesses ADPase and ATP- diphosphohydrolase activities (247). (C) 1999 Elsevier Science Ltd. All rig hts reserved.