Musca domestica CYP6A1 was the first insect P450 to be cloned, functionally expressed, purified and characterized (Feyereisen et al., 1989; Andersen et al., 1994; Guzov et al., 1996;Andersen et al., 1997; Sabourault et al., 2001; Jacobsen et al., 2006; Murataliev et al., 2008).

The role of CYP6A1 in diazinon resistance in the Rutgers strain of the house fly is discussed here.

CYP6A1 appears to be a rather promiscuous xenobiotic-metabolizing P450. The figure below shows some of the substrates and site of metabolism,

Information on substrate access to the active site and active site topology can also be inferred from spectral studies and biochemical studies.

The active site topology of CYP6A1 was studied by a technique developed in Ortiz de Montellano's group (Ortiz de Montellano and Graham-Lorence, 1993). The enzyme is first incubated with phenyldiazene to form a phenyl-iron complex. Ferricyanide-induced in situ migration of the phenyl group to the porphyrin nitrogens causes the formation of covalent adducts than can be separated by HPLC. The N-phenyl protoporphyrin IX adducts of CYP6A1 were formed in a 17:25:33:24 ratio of the NB:NA:NC:ND isomers (Andersen et al., 1997). Thus in the native protein, all four pyrrole groups are somewhat exposed, whereas in several other P450s, labeling is more specific. Specific labeling indicates that the protein encumbers more space on top of the heme prosthetic group, e.g. leaving only one pyrrole ring exposed as in P450scc (Pikuleva et al., 1995). The type of labeling seen with CYP6A1 indicates less encumbrance by the protein on top of the heme as in CYP3A4 (Schrag and Wienkers, 2000).

These experiments suggest that the active site of CYP6A1 is relatively accessible and not severely constrained. Indeed CYP6A1 metabolizes flat steroids, bulky cyclodiene insecticides, as well as a variety of sesquiterpenoids (Andersen et al., 1994, 1997, Jacobsen et al., 2006; Murataliev et al., 2008). High uncoupling of electron transfer relative to monooxygenation may be a result of this broad substrate specificity.