BBB seminar: Michael R. Duchen
Mitochondria as ATP consumers; the cell biology of the endogenous inhibitory protein IF1
Michael R. Duchen
Departments of Medicine and Physiology, University College London, UK
The protein IF1, known as the ‘endogenous inhibitor of the mitochondrial ATPase’ (Pullman and Monroy, 1963 JBC, 238:3762-9) inhibits ATPase activity at an acidic pH in studies of the isolated enzyme. It has therefore been thought to protect cells from mitochondrial ATP consumption during pathological states such as ischaemia and reperfusion injury by inhibiting the ATP synthase in its ‘reverse mode’ (Green and Grover, 2000 BBA, 1458(2-3):343-55). As its impact on mitochondrial function in intact cells is not established, we have explored the effect of overexpression or knockdown of IF1 in c2c12 and HeLa cell lines. We found that in response to inhibition of respiration, IF1 conserves ATP (measured using luciferase transfected into the cells) at the expense of mitochondrial depolarisation. Knocking down the protein promoted conservation of mitochondrial potential at the expense of ATP. Surprisingly, IF1 also has a profound impact on mitochondrial structure and function: IF1 overexpression increased mitochondrial mass and ATP synthase activity, decreasing the mitochondrial membrane potential and favouring a relative dependence of ATP homeostasis on oxidative phosphorylation. Knocking down the protein had the opposite effect. These observations show that IF1 has an influence on mitochondrial function at rest and that it is effective at preserving cellular ATP in hypoxic or ischaemic conditions.
Host: Karl Johan Tronstad <karl.tronstad[@]biomed.uib.no>, Dept. of Biomedicine