Distribution of Flux Control among the Enzymes of Mitochondrial Oxidative Phosphorylation in Calcium‐activated Saponin‐skinned Rat Musculus Soleus Fibers

Abstract

Metabolic control analysis was applied to describe the control of mitochondrial oxidative phosphorylation in calcium (approximately 2 μM free calcium) activated saponin‐skinned rat musculus soleus fibers oxidizing glutamate and malate. Under these circumstances approximately 80% of mitochondrial active‐state respiration was reached due to the activation of ATP turnover by actomyosin ATPase. The flux control coefficients of H+‐ATPase, adenine‐nucleotide translocase, phosphate transporter, NADH:ubiquinone oxidoreductase and cytochrome‐c oxidase were determined to be equal to 0.16 ± 0.08 (n= 6), 0.34 ± 0.12 (n= 5), 0.08 ± 0.03 (n= 5), 0.01 ± 0.006 (n± 4) and 0.09 ± 0.03 (n= 3) using inhibitor titrations with the specific inhibitors oligomycin, carboxyatractyloside, mersalyl, rotenone and cyanide, respectively, and applying non‐linear regression of the entire titration curve. The flux control coefficient of actomyosin ATPase was determined with vanadate to be equal to 0.50 ± 0.09 (n= 6), measuring independently the vanadate‐caused inhibition of fiber respiration and ATP‐splitting activity. In contrast to results with isolated rat skeletal muscle mitochondria reconstituted with soluble F1‐ATPase the decrease in phosphate concentration from 10 mM to 1 mM only slightly affected the distribution of flux control coefficients. This difference is caused by different kinetic properties of soluble F1‐ATPase and actomyosin ATPase. Therefore, phosphate seems to be in skeletal muscle in vivo only a modest modulator of control of oxidative phosphorylation. Copyright © 1995, Wiley Blackwell. All rights reserved