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Abstract
The dominant cytochrome in thiosulphate-grown Thiobacillus A2 was found to be of the c-type with a reduced α-band at 548 nm (c 548). This c 548 component did not constitute an integral part of the membrane carrier system. It did, however, appear to be part of a large complex not tightly bound to membranes. Reconstitution experiments showed that cytochromes of the membrane ‘abc’ system could be reduced by the c 548 component and vice versa. The reduction of membrane cytochromes of either lithotrophic or organotrophic origin by thiosulphate electrons was achieved, but it required the presence of a soluble fraction containing cytochrome c 548. Evidence tending to rule out a reductive cleavage as the first step of the thiosulphate oxidation pathway in Thiobacillus A2 was obtained by following the reduction of partially purified c 548 particles under various conditions.
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