2',3'-cyclic nucleotide 3'-phosphohydrolase in rat liver mitochondrial membranes

2',3'-Cyclic nucleotide 3'-phosphohydrolase (nucleoside-2':3'-cyclic-phosphate 2'-nucleotidohydrolase, EC 3.1.4.37) activity has been demonstrated in rat liver mitochondria. The enzyme was localized in both the outer and inner mitochondrial membranes but was absent from the intermembrane space and matrix. The mitochondrial (cyclic nucleotide) phosphohydrolase was activated by freezing and thawing and by treatment with digitonin or detergents. It is suggested that (cyclic nucleotide) phosphohydrolase is an integral membrane protein which is buried to a significant degree within the membrane. Atractyloside was found to be a noncompetitive inhibitor of the enzyme both in intact mitochondria and in preparations of the mitochondrial membranes. The enzyme substrate, 2',3'-cyclic adenosine monophosphate, had no effect on the oxidation of exogenous beta-hydroxybutyrate or succinate by intact mitochondria. These findings suggest that 2',3'-cyclic nucleotide 3'phosphohydrolase is more widely distributed than was previously thought and that the enzyme may play a fundamental role in membranes, independent of their specialized structure or functions.