Effect of amytal, pyridine nucleotides, and oxaloacetate on the respiratory inhibition-activation cycles in mitochondria

Abstract

Rat liver mitochondria which were not able to show spontaneous oscillations of the respiratory intensity responded in the usual cyclic manner after addition of low concentrations of oxaloacetate. Amytal added to mitochondrial systems in which oxygen uptake had been inhibited, abruptly increased the respiratory rate. After a short period of active respiration, a gradual decline of oxygen utilization ensued. With amytal added from zero time respiration occurred at a high rate for a longer time than in its absence, the same steady decline being noted afterwards. In the presence of NAD the first inhibition of the respiration began earlier than in its absence or when NADH 2 was added instead of NAD. The subsequent pattern of oxygen uptake, both in the presence of NAD as of NADH 2, presented less fluctuation. In the absence of ATP no oscillations of respiration but a gradual decline down to low values was obtained. One m M NAD or 1 m M NADH 2, when present from zero time, re-established the cyclic course of respiration. One half to 2 m M ATP, added after the onset of inhibition, caused a marked increase in the rate of oxygen uptake. Amytal was less effective in stimulating oxygen uptake in these systems than was ATP.