PURIFICATION AND ENZYMATIC IDENTITY OF MITOCHONDRIAL CONTRACTION-FACTORS I AND II

Abstract

"Contraction factor" of rat liver mitochondria, which is required for ATP-linked reversal of glutathione-induced water uptake, has been resolved into three components by chromatographic procedures, and each has been substantially purified. C-factor I has been identified as the enzyme glutathione peroxidase and C-factor II as catalase; C-factor HI, which is heat-stable and is apparently a small molecule, remains unidentified as to its enzymatic activity. Highly purified specimens of glutathione peroxidase from erythrocytes and crystalline beef liver catalase show all the properties of mitochondrial C-factors, including (a) activity in supporting ATP-linked reversal of glutathione-swelling, (b) inhibition of glutathione-induced mitochondrial swelling, (c) mandatory sequence of action on mitochondria with ATP, and (d) ability to increase the P:O ratio of oxidative phosphorylation in digitonin fragments. The function of glutathione peroxidase and catalase in promoting mitochondrial contraction appears not to be due primarily to the removal of any toxic accumulations of hydrogen peroxide; added hydrogen peroxide does not significantly stimulate swelling or inhibit ATP-linked contraction, even in very high concentrations. It appears more likely that catalase and glutathione peroxidase are concerned either in the formation and removal of lipid peroxides or in the mechanism of electron transport, to which the mechanochemical changes of swelling and contraction are coupled.