title: Alternative hydroxylases for the aerobic and anaerobic biosynthesis of ubiquinone in Escherichia coli.
abstract: The synthesis of ubiquinone under anaerobic conditions was examined in a variety of strains of Escherichia coli K12. All were shown to synthesize appreciable quantities of ubiquinone 8 when grown anaerobically on glycerol in the presence of fumarate. Under these conditions, ubiquinone 8 was in most cases the principal quinone formed, and levels in the range 50--70% of those obtained aerobically were observed. Studies with mutants blocked in the various reactions of the aerobic pathway for ubiquinone 8 synthesis established that under anaerobic conditions three alternative hydroxylation reactions not involving molecular oxygen are used to derive the C-4, -5, and -6 oxygens of ubiquinone 8. Thus, mutants blocked in either of the three hydroxylation reactions of the aerobic pathway (ubiB, ubiH, or ubiF) are each able to synthesize ubiquinone 8 anaerobically, whereas mutants lacking the octaprenyltransferase (ubiA), carboxy-lyase (ubiD), or methyltransferases (ubiE or ubiG) of the aerobic pathway remain blocked anaerobically. The demonstration that E. coli possesses a special mechanism for the anaerobic biosynthesis of ubiquinone suggests that this quinone may play an important role in anaerobic metabolism.
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D004926:Escherichia coli / Q000201:enzymology*; D005650:Fumarates / Q000378:metabolism; D005838:Genotype; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D013045:Species Specificity; D014451:Ubiquinone / Q000096:biosynthesis*
chemical_list: D005650:Fumarates; D014451:Ubiquinone; D006899:Mixed Function Oxygenases