The mechanism of alpha-ketoisocaproate oxygenase. Formation of beta-hydroxyisovalerate from alpha-ketoisocaproate.
A soluble alpha-ketoisocaproate oxygenase from rat liver catalyzes the decarboxylation and hydroxylation of alpha-ketoisocaproate to form beta-hydroxyisovalerate. The source of oxygen (O2 or H2O) enzymatically incorporated into beta-hydroxyisovalerate was investigated using 18O2 and H218O. Greater than 92% of the carboxyl groups of beta-hydroxyisovaleric acid contained 1 18O atom from 18O2 and 15% of the beta-hydroxyl oxygens of beta-hydroxyisovaleric acid contained 18O from 18O2. Since some oxygen of the beta-hydroxyl group is derived from O2 and since others have shown a rapid H2O in equilibrium ROH exchange for similar reactions, we conclude that both of the oxygens of beta-hydroxyisovaleric acid are derived from O2 and that exchange of water oxygen with the beta-hydroxyl group of beta-hydroxyisovaleric acid must occur with an intermediate of the reaction. Thus, the alpha-ketoisocaproate oxygenase would be a dioxygenase. A mechanism consistent with the 18O experiments and other properties of the enzyme is proposed.
D000818:Animals; D002208:Caproates / Q000378:metabolism*; D049308:Dioxygenases; D007651:Keto Acids / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D013058:Mass Spectrometry; D010103:Oxygen Isotopes; D010105:Oxygenases / Q000378:metabolism*; D051381:Rats; D014631:Valerates / Q000378:metabolism*
D002208:Caproates; D007651:Keto Acids; D010103:Oxygen Isotopes; D014631:Valerates; C004961:beta-hydroxyisovaleric acid; C013082:alpha-ketoisocaproic acid; D010105:Oxygenases; D049308:Dioxygenases; C034776:alpha-ketoisocaproate oxygenase