Pyruvate oxidation and the permeability of housefly sarcosomes

Abstract

Housefly sarcosomes have been shown to oxidize added pyruvate by way of the Krebs cycle. This oxidation occurred in the absence of added Krebs-cycle intermediates and in the absence of carboxylating reactions that might have formed malate or oxaloacetate from the added pyruvate. Various conditions that have to be fulfilled before this unique phenomenon can occur are discussed. The inability of 2,4-dinitrophenol to stimulate pyruvate oxidation in the absence of adenosine diphosphate or inorganic phosphate is explained by the requirement for these compounds of the substrate-level phosphorylation coupled to the oxidation of [alpha]-oxoglutarate. Additional evidence is presented in support of the suggested permeability barrier in the sarcosomes towards externally added substrates. It is suggested that the physiological function of this barrier might be to prevent the Krebs-cycle intermediates from leaking out of the sarcosomes. Isolated housefly sarcosomes oxidize glutamate via the glutamate-dehydrogenase pathway, although glutamate-oxaloacetate transaminase is present in the sarcosomes and is active towards external glutamate and oxaloacetate.