[Properties of reconstituted transhydrogenase from mitochondria]

The membrane vesicles (proteoliposomes) have been reconstituted from soya bean phospholipids and mitochondrial transhydrogenase (EC 1.6.1.1) by a self-assembly procedure. Palmitoyl-CoA and Mg2+ inhibit the rate of NAD+ reduction by NADPH in these proteoliposomes as well as in these submitochondrial particles. After solubilization of transhydrogenase from submitochondrial particles membranes the specific activity of the enzyme decrease and then again increases (more than 4.5 times) after its incorporation into the proteoliposomal membranes. An addition of potassium cholate to the proteoliposomal suspension further increases the rate of the direct transhydrogenase reaction (by 35--40%) due to the function of the oppositely oriented molecules of transhydrogenase. The Michaelis constants for NAD+ and NADPH for transhydrogenase proteoliposomes are 27 microM and 30 microM, respectively. These data are practically coincident with the results obtained for submitochondrial particles (21 and 33 microM, respectively). Thus, the incorporation of transhydrogenase into proteoliposomal membranes results in reconstitution of both electrogenic and the most essential kinetic properties of the enzyme.