Energy-linked reactions in mitochondria. Studies on the reduction of NAD+ by succinate.

Abstract

Summary 1. The ATP-dependent reduction of NAD + by succinate catalysed by submitochondrial particles prepared from beef, sheep and pig heart mitochondria has been examined 2. The general features of the reaction are similar to those described by other workers, especially the sensitivity of the reaction to inhibitors and uncouplers of respiration and oxidative phosphorylation such as 2,4-dinitrophenol, Amytal, rote-none and oligomycin 3. The stereospecificity of hydrogen transfer in the ATP-dependent reduction of NAD + has been investigated using [ 3 H]N AD + as the hydrogen acceptor and methods are described for the preparation and separation of tritiated pyridine nucleotides 4. Stereospecificity studies show that the terminal reductive step in the energy-linked reduction of NAD + by succinate is catalysed by an enzyme of B-specificity, possibly the NADH dehydrogenase (EC 1.6.99.3) flavoprotein system. These results also exclude malate dehydrogenase (EC 1.1.1.37), an enzyme of A-specificity, as a participant in the reaction.