GENERATION OF REDUCING POWER IN CHEMOSYNTHESIS .6. ENERGY-LINKED REACTIONS IN CHEMOAUTOTROPH, THIOBACILLUS NEAPOLITANUS

Electron donors such as thiosulfate, sulfite, and ascorbate have been shown to enter the respiratory chain of T. neapolitanus at the level of cytochrome c. The enzymatic oxidation of these substrates catalyzed by the cytochrome oxidase (E. C. 1.9.3.1.) of T. neapolitanus cell-free extracts was coupled to the generation of energy which could be utilized to drive the reverse electron flow from cytochrome c to pyridine nucleotides. The reduction of endogenous or added flavin by thiosulfate or ascorbate has been shown to be ATP-dependent; likewise the reduction of cytochrome b by these electron donors also required energy. The rate of ATP-driven reversal of electron transfer from cytochrome c to the pyridine nucleotides was much faster compared with the rate of electron reversal catalyzed by the substrate-linked generated energy. The pathway of energy-linked reversal of electron transfer from cytochrome c to pyridine nucleotides involved cytochrome b and flavoproteins. NADH oxidation by T. neapolitanus cell-free extracts is mediated by the flavoprotein and cytochrome systems and this process also appears to be coupled with energy generation. The NADH oxidase (NADH2: cytochrome c oxidoreductase) was partially inhibited by amytal or rotenone, antimycin A or HOQNO, and was relatively insensitive to cyanide or azide. © 1969 Swets & Zeitlinger.