Catalase: a tetrameric enzyme with four tightly bound molecules of NADPH.

Abstract

Catalases (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) from many species are known to be tetramers of 60,000-dalton subunits, with 4 heme groups per tetramer. Previous authors determined the amino acid sequence and 3-dimensional structure of bovine liver catalase. Studies of the regulation of the pentose phosphate pathway led the present authors to a search for proteins that bind NADP+ and NADPH in human erythrocytes. An unexpected result of that search was the finding that a major reservoir of bound NADPH in human erythrocytes is catalase. Each tetrameric molecule of human or bovine catalase contains 4 molecules of tightly bound NADPH. The binding sites have the relative affinities NADPH > NADH > NADP+ > NAD+. NADPH does not seem to be essential for the enzymic conversion of H2O2 to O2 and water but does provide protection of catalase against inactivation by H2O2.