TY - JOUR T1 - Disparity in Holoprotein/Apoprotein Ratios of Different Standards Used for Immunoquantification of Hepatic Cytochrome P450 Enzymes JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 1733 LP - 1736 DO - 10.1124/dmd.107.015743 VL - 35 IS - 10 AU - H. F. Perrett AU - Z. E. Barter AU - B. C. Jones AU - H. Yamazaki AU - G. T. Tucker AU - A. Rostami-Hodjegan Y1 - 2007/10/01 UR - http://dmd.aspetjournals.org/content/35/10/1733.abstract N2 - An analysis of reported hepatic abundances of CYP3A4 and 3A5 indicated that values determined by immunoquantification using commercially available, unpurified recombinant enzymes as standards are significantly lower than those determined using purified enzymes or human liver microsomes characterized with lysosomal peptides (CYP3A4: mean 45 versus 121 pmol/mg protein, p < 0.01; CYP3A5: mean 28 versus 83 pmol/mg protein, p < 0.05). When immunoquantifying cytochromes P450 (P450s), it is assumed that the holoprotein (holo)/apoprotein ratio is the same in the samples and the standard. Estimates of holo/apoprotein ratios from data reported for a range of P450s purified from human liver and non-commercial recombinant systems indicated less than complete and variable heme coupling dependent on enzyme and system. The American Society for Pharmacology and Experimental Therapeutics ER -