The respiratory activity and permeability of housefly sarcosomes

Abstract

Sarcosomes isolated from the thoracic muscle of the housefly can oxidize [alpha]-glycerophosphate and pyruvate at rates comparable with those calculated for the flying insect. This rapid oxidation is accom-panied by high P:O ratios in the absence of serum albumin and is to a large extent under control of the adenosine diphosphate concentration. Glutamate, reduced diphosphopyridine nucleotide and Krebs-cycle intermediates are oxidized at very much lower rates, accompanied by poor phosphorylation and by no measurable respiratory control. It is shown that this is due to permeability barriers for these substrates in the sarcosome. The addition of a supernatant fraction to sarcosomes which are oxidizing one of the latter substrates has a stimulatory effect on respiration, phosphorylation and respiratory control. It is shown that this stimulation is caused by the continuous formation of equimolecu-lar amounts of [alpha]-glycerophosphate and pyruvate from carbohydrate sources in the supernatant fraction.