UNSPECIFIED (1993) CYTOCHROMES IN THIOBACILLUS-TEPIDARIUS AND THE RESPIRATORY-CHAIN INVOLVED IN THE OXIDATION OF THIOSULFATE AND TETRATHIONATE. ARCHIVES OF MICROBIOLOGY, 160 (2). pp. 87-95. ISSN 0302-8933

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Abstract

Thiobacillus tepidarius was shown to contain cytochrome(s) c with absorption maxima at 421, 522 and 552 nm in room temperature reduced minus oxidized difference spectra, present at 1.1-1.2 nmol per mg dry wt and present in both membrane and soluble fractions of the cell. The membrane-bound cytochrome c (1.75 nmol per mg membrane protein) had a midpoint potential (Em, pH 7.0) of 337 mV, while the soluble fractions appeared to contain cytochrome(s) c with Em (pH 7.0) values of about 270 and 360 mV. The organism also contained three distinct membrane-bound b-type cytochromes (totalling 0.33 nmol per mg membrane protein), each with absorption maxima in reduced minus oxidized difference spectra at about 428, 532 and 561 nm. The Em (pH 7.0) values for the three cytochromes b were 8 mV (47.8% of total), 182 mV (13.7%) and 322 mV (38.5%). No a- or d-type cytochromes were detectable spectrophotometrically in the intact organism or its membrane and soluble fractions. Evidence is presented for both CO-binding and CO-unreactive cytochromes b or o, and CO-binding cytochrome(s) c. From redox effects observed with CO it is proposed that a cytochrome c donates electrons to a cytochrome b, and that a high potential cytochrome b or o may be acting as the terminal oxidase in substrate oxidation. This may be the '445 nm pigment', a photodissociable CO-binding membrane haemoprotein. Substrate oxidation was relatively insensitive to CO-inhibition, but strongly inhibited by cyanide and azide. Thiosulphate oxidation couples directly to cytochrome c reduction, but tetrathionate oxidation is linked (probably via ubiquinone Q-8) to reduction of a cytochrome b of lower potential than the cytochrome c. The nature of possible electron transport pathways in Thiobacillus tepidarius is discussed. One speculative sequence is: e- --> b8 --> b182 --> C270 --> C337 --> b322/c360 --> O2

Item Type:	Journal Article
Subjects:	Q Science > QR Microbiology
Journal or Publication Title:	ARCHIVES OF MICROBIOLOGY
Publisher:	SPRINGER VERLAG
ISSN:	0302-8933
Date:	August 1993
Volume:	160
Number:	2
Number of Pages:	9
Page Range:	pp. 87-95
Publication Status:	Published
URI:	http://wrap.warwick.ac.uk/id/eprint/21170

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