EFFECT OF HYDROXYLAMINE ON RESPIRATION AND OXIDATIVE PHOSPHORYLATION

Rat liver mitochondria were used to study the effect of hydroxylamine on respiration and oxidative phosphorylation with succinate or tetramethyl‐p‐phenylenediamine plus ascorbate as substrate, and ATP phosphohydrolase activities. With these substrates hydroxylamine inhibited respiration in state 3. Inhibition was released by various uncouplers of oxidative phosphorylation, including gramicidin and calcium ions. Respiration in state 4 was affected much less. Arsenate‐induced respiratory increase was effectively inhibited by hydroxylamine. Succinate oxidase activity in state 3 with ferricyanide as the electron acceptor was not inhibited by hydroxylamine. Oxidative phosphorylation, with succinate as substrate, was inhibited more than respiration by hydroxylamine, with a concomitant decrease in the P/O ratio. Oxidative phosphorylation during succinate oxidation by ferricyanide was not affected by hydroxylamine. 2,4‐Dinitrophenol‐ and carbonylcyanide p‐trifluoromethoxy phenylhydrazone‐induced ATPase activities were not affected by hydroxylamine. The magnesium‐stimulated ATPase of detergent‐disrupted mitochondria was strongly inhibited but the gramicidin‐induced ATPase of intact mitochondria was only inhibited by about 30%. Under non‐respiring conditions hydroxylamine induced no ATPase by itself. Our results indicate that the inhibition of oxidative phosphorylation by hydroxylamine is specific for coupling site 3, and in some ways resembles the effects of oligomycin. It is suggested that site specificity exists up to the level of X∼P in the partial reactions of oxidative phosphorylation. Copyright © 1969, Wiley Blackwell. All rights reserved