Unusual dehydrations in anaerobic bacteria: considering ketyls (radical anions) as reactive intermediates in enzymatic reactions.
Dehydratases have been detected in anaerobic bacteria which use 2-, 4- or 5-hydroxyacyl-CoA as substrates and are involved in the removal of hydrogen atoms from the unactivated beta- or gamma-positions. In addition there are bacterial dehydratases acting on 1,2-diols which are substrates lacking any activating group. These enzymes contain either FAD, or flavins + iron-sulfur clusters or coenzyme B12. It has been proposed that the overall dehydrations are actually reductions followed by oxidations or vice versa mediated by these prosthetic groups. Whereas the gamma-hydrogen of 5-hydroxyvaleryl-CoA is activated by a transient two-election alpha, beta-oxidation, the other substrates are proposed to require either a transient one-electron reduction or an oxidation to a ketyl (radical anion).
Buckel
W
W
Laboratorium für Mikrobiologie, Philipps-Universität, Marburg, Germany. buckel@mailer.uni-marburg.de
D000214:Acyl Coenzyme A / Q000378:metabolism*; D000838:Anions / Q000378:metabolism*; D001421:Bacteria, Anaerobic / Q000201:enzymology / Q000378:metabolism*; D006836:Hydro-Lyases / Q000378:metabolism; D015394:Molecular Structure; D010421:Pentanoic Acids / Q000378:metabolism; D014631:Valerates / Q000378:metabolism; D014867:Water / Q000378:metabolism
D000214:Acyl Coenzyme A; D000838:Anions; D010421:Pentanoic Acids; D014631:Valerates; D014867:Water; C013056:beta-hydroxyvaleric acid; C100417:5-hydroxyvaleric acid; C066370:4-hydroxybutyryl-CoA dehydratase; D006836:Hydro-Lyases