Restoration by Albumin of Oxidative Phosphorylation and Related Reactions

Abstract

Bovine serum albumin prevented the effects of pentachlorophenol, 2,4-dinitrophenol, and various other reagents upon oxidative phosphorylation, the orthophosphate-adenosine triphosphate exchange reaction, adenosine triphosphatase, and respiratory control of rat liver mitochondria. More significantly, albumin restored the capacity for oxidative phosphorylation and the ancillary reactions, including respiratory control, to mitochondria previously reacted with these compounds. Inhibition by gramicidin, oligomycin A, antimycin A, and rotenone was not counteracted by albumin. Oxidative phosphorylation of liver mitochondria uncoupled by the intraperitoneal injection of pentachlorophenol into rats was also restored by albumin. The circulating halophenol after injection was found associated with the albumin fraction of the plasma. The ability of albumin to prevent the deleterious action of the uncoupling reagents, and to restore function to mitochondria treated with them, resides in its capacity to bind these reagents and thereby remove them from the medium or from mitochondria. The beneficial effect is specific for serum albumin. Various other proteins and compounds were found to be ineffective. It was shown that 1 mole of bovine serum albumin can bind 5 moles of pentachlorophenol. Each of these 5 moles is not held with equal affinity, and reversible binding was readily demonstrated. Certain modified albumins, i.e. acetylated, or denatured by chemical or physical means, lost their capacity to bind pentachloro- or 2,4-dinitrophenol. Other modifications, such as blocking sulfhydryl or imidazole groups, did not alter the ability of albumin to bind pentachlorophenol. From these results, evidence is adduced that the native protein structure and especially free amino groups are involved in the protein-phenol interaction. A possible physiological role for the reversible binding of uncoupling reagents to proteins is discussed, as is the use of the phenomenon in studying mitochondrial function and structure.