Oxidation of Sulfur Compounds and Coupled Phosphorylation in the Chemoautotroph Thiobacillus neapolitanus

Author:

Saxena J.,Aleem M. I. H.

Abstract

The intact cells from T. neapolitanus oxidized thiosulfate completely to sulfate with the consumption of 2 mol O2/mol thiosulfate. The oxidation of thiosulfate by cell-free extracts was incomplete and resulted in the accumulation of tetrathionate. Aerobic treatment of the intact cells with thiosulfate caused a rapid increase in the cellular ATP content which was unaffected by the flavoprotein inhibitors and antimycin A but was strongly inhibited by uncouplers of oxidative phosphorylation. The oxidation of sulfide by intact cells and cell-free extracts appears to proceed via two stages: (1) a cellular-membrane-associated initial and rapid oxidation stage which was dependent upon sulfide concentration, and (2) a slower oxidation reaction stage which was catalyzed by the soluble cell-free fractions. The oxidation of sulfide and 2-mercaptoethanol by intact cells or cell-free extracts was coupled to ATP generation and the process was inhibited by the respiratory chain inhibitors such as amytal, antimycin A, and cyanide, as well as by pentachlorophenol and carbonyl cyanide m-chlorophenyl hydrazone. The oxidation of sulfide and 2-mercaptoefhanol by cell-free extracts yielded P/O ratios of 0.3 and 0.85, respectively. The intact cells (in the absence of added electron donors) were able to exhibit an acid-induced ATP formation from the phosphorylation of endogenous ADP which could be inhibited effectively by uncouplers of oxidative phorylation but was unaffected by respiratory chain inhibitors.

Publisher

Canadian Science Publishing

Subject

General Medicine

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