87] Energy-coupling in nonphosphorylating submitochondrial particles

Abstract

The energy-linked pyridine nucleotide transhydrogenase reaction can be used as a tool for the demonstration of energy-coupling in so-called “nonphosphorylating” submitochondrial electron transport particles. The approach is based on the concept that the energy-linked transhydrogenase reaction involves the utilization of a nonphosphorylated high-energy compound, which is an intermediate of the respiratory chain-linked oxidative phosphorylation system. In phosphorylating submitochondrial particles, the energy-linked transhydrogenase reaction can be driven by the respiratory chain, Rreaction (2), or ATP, reversal of reaction (3), at approximately equal capacities. In contrast, nonphosphorylating particles can derive energy for driving the energy-linked transhydrogenase reaction much less efficiently from ATP than from the respiratory chain. The phosphorylating efficiency of the various types of particles as measured with succinate as the substrate, and their energy-linked transhydrogenase activities with either succinate or ATP as the sucrose of energy is tabulated. The transhydrogenase reaction is assayed spectrophotometrieally in the presence of oxidized glutathione and glutathione reductase. Oligomyin stimulates the respiratory chain-driven pyridine nucleotides transhydrogenase reaction in nonphosphorylating particles, and the amount of oligomyein required for maximal stimulation is considerably smaller than that required for inhibition of the ATPase activity of the same particles.