Table 1.

Summary of mechanistic studies performed with recombinant CYP3A4 and CYP3A5 (Takakusa et al., Barbara et al., Chan et al.)

Mechanistic studies	CYP3A4	CYP3A5	Interpretation
GSH trapping	Yes	Yes	Indicates formation of electrophilic metabolite capable of covalent binding
GSH protection from inactivation	Data not available	Yes	Indicates electrophilic metabolite release from active site
Reversal of inactivation via dialysis	Data not available	No	Indicates non-covalent inactivation, likely via MI complex of the heme iron
Formation of Soret peak	Yes	No	Indicates coordination of heme iron through a metabolite-intermediate complex
Reduced CO difference spectroscopy	Yes	Yes	Decrease in absorbance at 450 nm indicates alkylation of heme or adduction of the apoprotein vicinal to the heme
Reversal of inactivation by ferricyanide	Yes	No	Reversal indicates a non-covalent inactivation; Absence of reversal indicates covalent adduction
Mass shift of intact protein by mass spectrometry	No	Data not available	Indicates covalent binding to apoprotein or heme