Subsystem: Terminal cytochrome d ubiquinol oxidases
This subsystem's description is:
In many bacteria, there is more than one terminal respiratory oxidase (for a recent review, see J. Bacteriol..2001; 183: 6151-6498). The best-characterized terminal oxidases are those that are homologous to the aa3-type cytochrome c oxidases of mitochondria. Almost all cyanobacteria, even those that are obligate photoautotrophs, contain membrane-bound enzymes capable of the oxidation of cytochrome c .
Terminal respiratory oxidases with sequence similarity to the cytochrome bd quinol oxidase, which is found in bacteria, have also been identified in cyanobacteria (Anabaena website http://www.kazusa.or.jp /cyano/anabaena/). In Synechocystis sp. strain PCC 6803, there are three terminal respiratory oxidases, two homologous of the cytochrome c oxidase of mitochondria and one putative quinol oxidase homologous to Escherichia coli cytochrome bd.
The respiratory chain in cyanobacteria is intimately linked to photosynthetic electron transport , and the only electron transport components not directly involved in photosynthesis are the terminal respiratory oxidases, which act as the terminal acceptors of the electron transport chains and are therefore the key enzymes of cyanobacterial respiration.
CydDC exports cysteine, crucial for redox homeostasis in the periplasm. Cysteine is exported from the Escherichia coli cytoplasm by CydDC, an ATP-binding cassette-type transporter required for cytochrome assembly.Pittman et al,J Biol Chem. 2002 Dec 20;277(51):49841-9. In Gram+ organisms it should not be required for bd cytochrome expression but they still exist. Function?? In a B. subtilis strain with cydABCD deleted, synthesis of cytochrome bd can be restored when the four genes are supplied on a plasmid. Overexpression of cydAB alone does not allow cytochrome bd to be produced even in a CydD mutant strain.
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