Generation of reducing power in chemosynthesis IV. Energy-linked reduction of pyridine nucleotides by succinate in Thiobacillus novellus

Abstract

• 1.

  1. The experiments described in this report have indicated that the reduction of NAD⁺ by succinate in Thiobacillus novellus is energy-dependent. By blocking the electron transport chain with antimycin A, the endergonic reduction of NAD⁺ by succinate required ATP. The pyridine nucleotide reduction involved the mediation of the flavoprotein system as Atabrine and Amytal inhibited the process.

• 2.

  2. Added mammalian cytochrome $\text{c}$ has been shown to couple with the electron transport chain of T. novellus thus effecting the catalysis of the generation of high-energy intermediates coupled to succinate oxidation in the absence of inorganic phosphate. The non-phosphorylated high-energy compounds thus can be generated either at coupling site II by oxidation of succinate with cytochrome $\text{c}$ as electron acceptor under anaerobic conditions, or at sites II and III under aerobic conditions, or at site III by the oxidation of ferrocytochrome $\text{c}$ involving electron transport to molecular oxygen through the cytochrome oxidase portion of the respiratory chain. In all cases the reduction of NAD⁺ was driven by the generated high-energy intermediates involving reversal of electron transfer from the cytochrome $\text{c}$ level.

• 3.

  3. The energy-dependent reduction of NAD⁺ by succinate involving reversal of electron transfer from the cytochrome $\text{c}$ level was sensitive to 2,4-dinitrophenol, dicumarol and arsenate. It was also inhibited by atabrine and Amytal. Antimycin A was effective in partial inhibition of the reversal of electron transfer. In addition malonate and cyanide were found to be potent inhibitors. The mechanism for the generation and utilization of energy for the reversed electron flow, is discussed.