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The alternative oxidase from Euglena gracilis
Author(s) -
THEISSEN URSULA,
HEBING PEER,
MARTIN WILLIAM
Publication year - 2005
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.2005.05202003_1_78.x
Subject(s) - alternative oxidase , euglena gracilis , euglena , biology , biochemistry , ubiquinol , respiratory chain , electron transport chain , oxidative phosphorylation , mitochondrion , trypanosoma brucei , salicylhydroxamic acid , cytochrome c oxidase , mitochondrial respiratory chain , chloroplast , enzyme , coenzyme q – cytochrome c reductase , cytochrome c , gene
The alternative oxidase (AOX) is an ubiquinol oxidase of the mitochondrial respiratory chain. AOX is an additional terminal oxidase; the electron flux to AOX branches from the classical electron‐transport chain at the level of the ubiquinone pool leading to the direct reduction of oxygen to water in a single four‐electron transfer step. O 2 reduction catalyzed by AOX is not coupled to proton pumping and hence not ATP‐producing. The energy is released as heat. AOX is specifically inhibited by salicylhydroxamic acid (SHAM), but is cyanide resistant. AOX was discovered in plant thermogenic tissues and all plant species tested to date can express the alternative pathway. It was long thought that AOX is specific to higher plants, but it is now turning up in many non‐photosynthetic eukaryotes. For example the bloodstream form of the protist Trypanosoma brucei brucei that lacks functional cytochromes, limits most of its energy metabolism to glycolysis while passing the reducing equivalents produced to water via a plant‐like alternative oxidase. It has also been reported that oxidative phosphorylation in the protist Euglena gracilis is supported by an alternative respiratory pathway in which an AOX is involved. We have cloned the mitochondrial AOX from Euglena and have investigated the evolutionary history of this enzyme in prokaryotes and eukaryotes.