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Electron transfer kinetics of soluble fragments indicate a direct interaction between complex III and the caa3 oxidase in Thermus thermophilus
Author(s) -
Janzon Julia,
Ludwig Bernd,
Malatesta Francesco
Publication year - 2007
Publication title -
iubmb life
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.132
H-Index - 113
eISSN - 1521-6551
pISSN - 1521-6543
DOI - 10.1080/15216540701242482
Subject(s) - thermus thermophilus , paracoccus denitrificans , electron transfer , cytochrome c oxidase , thermophile , electron transport chain , cytochrome , chemistry , kinetics , cytochrome c , respiratory chain , electron transport complex iv , ionic strength , oxidase test , stereochemistry , biochemistry , photochemistry , enzyme , mitochondrion , organic chemistry , escherichia coli , physics , quantum mechanics , aqueous solution , gene
The extremely thermophilic bacterium Thermus thermophilus expresses an aerobic respiratory chain resembling that of mitochondria and many mesophilic prokaryotes. Yet, interaction modes between redox partners differ between the thermophilic and mesophilic electron transport chains. While electron transfer in mesophilic organisms such as Paracoccus denitrificans follows a two‐step mechanism mostly governed by long‐range electrostatic interactions, the electron transfer in thermophiles is mediated mainly by apolar interactions. The terminal branch of the electron path from the bc‐complex via the soluble cytochrome c552 to the ba3 oxidase has extensively been characterized, whereas contradicting evidence has been put forward on the nature of the physiological substrate(s) of the caa3 oxidase. We have cloned and expressed a soluble fragment of the hydrophilic cytochrome c domain derived from subunit IIc of the caa3 oxidase (ccaa3) and characterized its kinetic behaviour in terms of substrate specificity and ionic strength dependency using pre‐steady state stopped‐flow techniques. The kinetics revealed fast electron transfer between the caa3 fragment and both, the cytochrome c552 and the soluble cytochrome cbc fragment of the bc‐complex, showing only a weak ionic strength dependence. These data suggest a direct intercomplex electron transfer between the bc‐complex and the caa3 oxidase without requirement for a soluble electron shuttle.