Oxidative phosphorylation and the Pi-ATP exchange reaction of submitochondrial particles under the influence of organic solvents.

M Tuena De Gómez-Puyou,G Ayala,A Darszon,A Gómez-Puyou

doi:10.1016/s0021-9258(17)42724-4

Abstract

The effect of some organic solvents, in particular dimethyl sulfoxide, on oxidative phosphorylation, the Pi-ATP exchange reaction, and ATP hydrolysis has been studied in submitochondrial particles from bovine heart. The three reactions are inhibited by dimethyl sulfoxide, but with a different sensitivity. Oxidative phosphorylation takes place at considerable rates in the presence of concentrations of dimethyl sulfoxide that completely inhibit the Pi-ATP exchange reaction. The sensitivity of the Pi-ITP exchange reaction to dimethyl sulfoxide measured in the presence of electron transport is also higher than that of oxidative phosphorylation. Dimethyl sulfoxide inhibits an electrochemical H+ gradient-dependent stimulating effect of inorganic phosphate on ATP hydrolysis which is linked to the Pi-ATP exchange reaction. In the absence of phosphate or in the presence of phosphate plus uncoupler, dimethyl sulfoxide does not inhibit hydrolysis. These findings, together with the observation that electron transport increases the rate of the Pi-ITP exchange reaction, suggest that electrochemical H+ gradients modify the kinetic characteristics of particulate Fi-ATPase. Glycerol and methanol, but not dimethylformamide, induce effects similar to those of dimethyl sulfoxide on oxidative phosphorylation and the Pi-ATP exchange reaction. This suggests that the described effects of solvents could be due to alterations of water structure.

Highlights

Oxidative Phosphorylation and the Pi-ATP Exchange Reaction of Submitochondrial Particles under the Influence of Organic Solvents*
The effect of some organic solvents, in particular dimethyl sulfoxide, on oxidative phosphorylation, the Pi-ATP exchange reaction, and ATP hydrolysis has been studied in submitochondrial particles from bovine heart
Dimethyl sulfoxide inhibits an electrochemical H+ gradient-dependent stimulating effect of inorganic phosphate on ATP hydrolysis which is linked to the Pi-ATP exchange reaction

Summary

MATERIALS AND METHODS

Bovine heart mitochondria were prepared as described by Low and Vallin [8];“heavy mitochondria” were stored at -30 “Cuntil use. For measurements of 32P,incorporated into ATP, an aliquot of the supernatant (usually 0.4 ml) was taken to 1.5 ml with water, and supplemented with 1 ml of 3.3% ammonium molybdate and 3.8 N HzS04;this mixture was extracted five times with butyl acetate. [Y-~'P]ATPwas prepared with the purified 3zP,according to Glynn and Chappell(l3).In the experiments with dimethyl sulfoxide, dimethylformamide, glycerol, and methanol, the incubation mixtures were adjusted to within 0.02 pH unit with a combination pH electrode in a Beckman expanded pH meter. Their concentration is expressed as percentage (v/v) of solvent added. Protein was determined by the biuret method with bovine serum albumin as standard

RESULTS

Findings

DISCUSSION