Inhibition of Formation of Adenosine Triphosphate in Thiobacillus thioparus by 2 : 4-Dinitrophenol

Abstract

ENZYMES in cell-free extracts of Thiobacillus thioparus catalyse the reduction of thiosulphate to sulphide and sulphite. Sulphite is then oxidized to sulphate and adenosine diphosphate produced in a coupled substrate phosphorylation which is not inhibited by 2:4-dinitrophenol^1,2. Comparison of the dinitrophenol inhibition of carbon dioxide fixation when either thiosulphate or sulphide was oxidized by intact cells of T. thioparus suggested that both dinitrophenol-sensitive and dinitrophenol-insensitive phosphorylations were coupled to thiosulphate oxidation³. We now present direct evidence from ATP analyses which shows that phosphorylation coupled to thiosulphate oxidation is much less sensitive to dinitro-phenol inhibition than that coupled to sulphide oxidation.