Proposed mechanism for the cytochrome P450-catalyzed conversion of aldehydes to hydrocarbons in the house fly, Musca domestica.

Experiments were performed to elucidate the mechanism of hydrocarbon formation in microsomal preparations from the house fly, Musca domestica. Antibody to both house fly cytochrome P450 reductase and a purified cytochrome P450 (CYP6A1) from the house fly inhibited (Z)-9-tricosene (Z9-23:Hy) formation from [15,16-3H]-(Z)-15-tetracosenal (24:1 aldehyde). Chemical ionization-gas chromatography-mass spectrometry (CI-GC-MS) analyses of the n-tricosane formed by microsomal preparations from [2,2-2H2,2-13C]- and [3,3-2H2,3-13C]tetracosanoyl-CoA demonstrated that the deuteriums on the 2,2- and 3,3-positions were retained in the conversion to the hydrocarbon product. Likewise, CI-GC-MS analysis of the Z9-23:Hy formed from [1-2H]tetracosenal by microsomal preparations demonstrated that the aldehydic proton on the 1-carbon was transferred to the hydrocarbon product. Hydrogen peroxide, cumene hydroperoxide, and iodosobenzene were able to support hydrocarbon production from [3H]24:1 aldehyde in place of O2 and NADPH for short incubation times. From these data, a cytochrome P450 mechanism is proposed in which the perferryl iron-oxene, resulting from heterolytic cleavage of the O-O bond of the iron-peroxy intermediate, abstracts an electron from the C=O double bond of the carbonyl group of the aldehyde. The reduced perferryl attacks the 1-carbon of the aldehyde to form a thiyl-iron-hemiacetal diradical. The latter intermediate can fragment to form an alkyl radical and a thiyl-iron-formyl radical. The alkyl radical then abstracts the formyl hydrogen to produce the hydrocarbon and CO2.