A comparison of the phosphorylation potential and electrochemical proton gradient in mung bean mitochondria and phosphorylating sub-mitochondrial particles

Abstract

The phosphorylation potential (delta Gp) and the electrochemical proton gradient (delta muH+) normally maintained during respiration or ATP hydrolysis by mung bean hypocotyl mitochondria and phosphorylating sub-mitochondrial particles have been investigated. Phosphorylation potential experiments using safranine and oxonol-VI, as membrane potential markers for mitochondria and sub-mitochondrial particles, respectively, suggest that the 'null point' delta Gp (i.e., the phosphorylation potential at which no change in optical signal occurred) corresponds to a value of 15.2 +/- 0.7 kcal/mol in mitochondria and 11.2 +/- 0.3 kcal/mol in sub-mitochondrial particles. The value of delta muH+ generated by the hydrolysis of ATP was estimated using ion distribution techniques. In each case a rapid centrifugation technique was used to separate the organelle from the suspending medium. The total delta muH+ generated in each case was approx. 200 mV being composed of both membrane potential and pH components. A comparison of delta muH+ with delta Gp indicates that the apparent H+/ATP ratio in mung bean mitochondria is 3.4 +/- 0.2 while in phosphorylating sub-mitochondrial particles it is 2.2 +/- 0.1.