A revised and more detailed hypothesis for the mechanism of oxidative phosphorylation at the diphosphopyridine nucleotide— Flavin level

Abstract

A revised hypothesis is given for the mechanism of the conservation of energy gained at the flavin level of the respiratory chain. It is assumed that an organic-bound phosphate group is activated and bound to the isoalloxazine ring, when DPNH † † The following abbreviations are used: for diphosphopyridine nucleotide in reduced form DPNH and in oxidized form DPN +; for flavin-adenine nucleotide in reduced form FADH 2 and in oxidized form FAD; for adenosine diphosphate and triphosphate ADP and ATP; for 2,4-dinitrophenole DNP; for inorganic phosphate P 1. is oxidized by FAD, in the same manner as was proposed earlier for the inorganic phosphate ion ( Grabe, 1958). The DPN + formed is assumed to be bound to N(1) of the imidazole ring of a histidine molecule either in oxidized form or after reduction by substrate, and when the flavin complex is oxidized by the next carrier the phosphoryl group should be transferred to the carboxyl group of the histidine or to a free carboxyl group of the energy transfer protein which is in close association with the histidine. The phosphoryl group is then displaced by the thiol group of the protein. When a P 1 ion attacks the C atom of COS, a DPN-histidine phosphate complex is formed. An intramolecular transfer of the phosphoryl group occurs when N(3) of the imidazole ring attacks the P atom, DPN being released. The phosphohistidine formed reacts with ADP, forming ATP and histidine. The hypothesis is concordant with the most significant experimental data concerning oxidative phosphorylation, the exchange reactions and the effects of inhibitors and uncouplers.