Disodium tetrachloropalladate (Na2PdCl4), an inhibitor of rat liver mitochondrial electron transport.

The effects of Na2PdCl4 were studied on isolated rat liver mitochondrial electron transport and oxidative phosphorylation in vitro. Significant reductions in ADP-stimulated respiration were observed with increasing Na2PdCl4 concentrations with both succinate and NADH-linked substrate oxidations. Concentration necessary for half-maximal inhibition of oxygen uptake (EC50) for an NADH-linked substrate system was 18 muM while with succinate as substrate the EC50 was 15 muM. At 64 muM both systems were inhibited maximally at 60 and 80%, respectively. At concentrations of Na2PdCl4 sufficient to inhibit acceptor-stimulated oxygen uptake, there was a concomitant decrease in the rate of ADP phosphorylation as measured by proton absorption. Uncoupling agents had no effect on Na2PdCl4 inhibited mitochondria. Mg-ATPase activity and phosphate acceptor limited (State 4) respiratory activity were not stimulated by any Na2PdCl4 concentration used in these investigations. Data from these experiments indicate that Na2PdCl4 inhibits the mitochondrial respiratory chain in vitro.