The energy-dependent accumulation of phosphate by blowfly mitochondria and its effect on the rate of pyruvate oxidation

Abstract

During an investigation of the kinetic properties of the NAD-linked isocitrate dehydrogenase (NAD-IDH) of mitochondria derived from the thorax of $\text{Caliphora vomitora}$ (a species of blowfly) it became apparent that this enzyme was inhibited by ATP and NADH₂ and was activated by ADP, Mg²⁺, isocitrate and phosphate. A particularly striking feature was the dependence on phosphate. A plot of activity $\text{versus}$ concentration resulted in a sigmoidal curve. At 5mM phosphate the enzyme produced 4–5% of its maximal activity and at 30mM 80%. Sacktor & Hurlbut (1966) have reported that at rest the phosphate content of whole blowfly thorax is 6.8μmoles/gm. wet wt. and in activity 7.5μmoles/gm.