Generation of reducing prower in chemosynthesis

Summary

Cell-free preparations from T. neapolitanus catalyzed an ATP-dependent reduction of pyridine nucleotides by thiosulfate. The reduction of flavins by thiosulfate was also observed to be an energy-linked process. Optimal reaction occurred at pH 7.3–7.5 in the presence of 7 mM S₂O₃ ⁼, 1.5 mM ATP and 0.7 mM NAD⁺ or NADP⁺. The enzyme(s) catalyzing the energy-linked reactions appear to reside in the 144000 x g supernatant fraction since washed particles failed to catalyze the ATP driven NAD⁺ reduction by S₂O₃ ⁺; the cell-free preparations contained, however, S₂O₃ ⁼ oxidase and ferro-cytochrome c: O₂ oxidoreductase activities. The ATP-driven reduction of flavins or that of the pyridine nucleotides was inhibited bythe inhibitors that intersect the electron transport chain in the flavin or that of the cytochrome b and c regions. In the flavin-inhibited system, quinones could substitute as electron bypass carriers for the reduction of pyridine nucleotides. Uncouplers of oxidative phosphorylation and oligomycin inhibited the energy-transfer reactions. A utilization of 2 to 3 ATP equivalents was observed for the reduction of each equivalent of NAD⁺. Such observations indicate that the T. neapolitanus system operated with an efficiency of approximately 80% with respect to the utilization of energy for the generation of reducing power.