The respiratory metabolism of insect flight muscle. I. Manometric studies of oxidation and concomitant phosphorylation with sarcosomes

Abstract

Oxidation and concomitant phosphorylation in mitochondria (sarcosomes) from flight muscle of the fly, Musca domestica, were characterized by manometric techniques. It was found that the highest respiratory rate was obtained with α-glycerophosphate. With this substrate a Q o 2 twice that for succinate was recorded. P/O values were determined for several substrates. Ratios between 1.0 and 1.7 were observed for α-glycerophosphate and succinate. Ratios greater than 2.0 were found for glutamate and α-ketoglutarate. The oxidative phosphorylation potential of various reaction mixtures was assayed. Replacement of isotonic saline with sucrose in the incubation medium increased the P/O. Fluoride caused a small decrease in respiration when the sarcosomes were isolated in 0.25 M sucrose, but not when 0.25 M sucrose plus ethylenediamine tetraacetate was used. Fluoride had no appreciable effect on phosphorylation except in the experiments with glutamate. With this substrate, inorganic phosphate uptake was markedly inhibited. Malonate lowered the respiratory rate slightly, but the P/O was increased. The optimal hexokinase concentration was determined. The influence of the phosphate acceptor system on oxidative phosphorylation was measured. These preparations showed no respiratory control, for the respiratiory rate was independent of the concentration of adenine nucleotide. Phosphorylation, however, was dependent on the nucleotide. Nucleosides and nucleotides other than adenosine 5-mono-, di-, and triphosphates were not suitable phosphate acceptors. Dinitrophenol uncoupled oxidative phosphorylation. Oxygen uptake was never stimulated. A heterogeneity in the dinitrophenol-sensitive phosphorylation was described. The efficiency of a given concentration of this inhibitor was apparently modified by the substrate metabolized. The high level of α-glycerophosphate oxidation in insects is particularly associated with flight muscle.