THE ROLE OF MAGNESIUM IN THE OXIDATION OF EXTERNAL REDUCED NICOTINAMIDE ADENINE DINUCLEOTIDE BY RAT LIVER MITOCHONDRIA

The oxidation of added dihydro-nicotinamide-adenine dinucleotide (NADH) by rat liver mitochondria in the presence of different concentrations of magnesium was studied.It was found that, in the absence of added magnesium, NADH was oxidized rapidly by isolated rat liver mitochondria. The addition of either magnesium or ATP strongly inhibited the oxidation of NADH.The inhibition of NADH oxidation induced by magnesium was not released by the addition of a phosphate acceptor, but it was partially released by the addition of ATP at concentrations lower than that of magnesium. As the concentration of ATP increased over that of magnesium, its releasing effect tended to disappear.Similarly, the inhibition of NADH oxidation induced by ATP was partially released by the addition of magnesium at concentrations lower than that of ATP. As the magnesium concentration increased over that of ATP, its releasing effect diminished and eventually caused a greater inhibition than that produced by ATP alone.It is suggested that conditions similar to those described in the oxidation of added NADH by isolated rat liver mitochondria might also occur in the intact cell.