Adenine Nucleotide Translocation in Mitochondria: Quantitative Evaluation of the Correlation between the Phosphorylation of Endogenous and Exogenous ADP in Mitochondria

Abstract

A detailed kinetic analysis of partial reactions of oxidative phosphorylation has been carried out. The uncoupler‐stimulated hydrolysis of endogenous ATP appears to be a first order reaction with respect to ATP. Respiration‐linked phosphorylation of endogenous ADP can be described as a reversible reaction consisting of first order forward (ADP phosphorylation) and backward (ATP hydrolysis) reaction. The steady state ratio of endogenous ATP to ADP equals the ratio of the two first order reaction constants. The activity of adeine nucleotide translocation is assayed parallel to oxidative phosphorylation. From these results and our present knowledge of the properties of translocation, the steady state level of endogenous ADP and the rate of the phosphorylation of exogenous ADP is calculated. It is possible to compute the entire time couse of the phosphorylation of endogenous and exogenous ADP. The calculated values agree rather well with the measurements. Even a lag period appearing in the measure time course of ATP synthesis is reproduced by calculation and well explained. It is concluded that the endogenous adenine nucleotides are in a state as if in free solution. There is no indication that part of the endogenous ADP and ATP might be in a different compartment. The role of adenine nucleotide translocation in securing a minimal potential of an energyrich state in the mitochondria is discussed. Copyright © 1969, Wiley Blackwell. All rights reserved