Energy-linked reactions in mitochondria: studies on the mechanism of the energy-linked transhydrogenase reaction.

Abstract

Summary 1. The mechanism of both the energy-linked and non-energy-linked trans-hydrogenase reaction catalysed by submitochondrial particles from beef-heart mitochondria has been examined using 3 H- and 14 C-labelled pyridine nucleotides as substrates. 2. The energy-linked transhydrogenase reaction does not proceed via a net group transfer of either the adenine or nicotinamide moieties or of phosphate from one pyridine nucleotide to another. 3. Studies with 3 H-labelled pyridine nucleotides show conclusively that in the energy-linked transhydrogenase reaction hydrogen is transferred directly from the A locus of NADH to the B locus of NADP + , i.e . the energy-linked transhydrogenase is an A:B transhydrogenase involving direct hydrogen transfer. 4. Studies on the non-energy-linked transhydrogenase show conclusively that the stereochemistry of the non-energy-linked reaction is identical to that of the energy-linked transhydrogenase reaction. 5. When the reaction is carried out in tritiated water there is only a low incorporation of tritium into NADPH thus confirming that the reaction is one involving direct hydrogen transfer.