title: Disparity in holoprotein/apoprotein ratios of different standards used for immunoquantification of hepatic cytochrome P450 enzymes.
abstract: 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.
authors.affiliation: Academic Unit of Clinical Pharmacology, University of Sheffield, Royal Hallamshire Hospital, Sheffield, UK.
authors.forename: H F
authors.initials: HF
authors.lastname: Perrett
authors.forename: Z E
authors.initials: ZE
authors.lastname: Barter
authors.forename: B C
authors.initials: BC
authors.lastname: Jones
authors.forename: H
authors.initials: H
authors.lastname: Yamazaki
authors.forename: G T
authors.initials: GT
authors.lastname: Tucker
authors.forename: A
authors.initials: A
authors.lastname: Rostami-Hodjegan
mesh_terms: D000328:Adult; D001059:Apoproteins / Q000032:analysis* / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008862:Microsomes, Liver / Q000201:enzymology*; D011994:Recombinant Proteins / Q000032:analysis / Q000378:metabolism
chemical_list: D001059:Apoproteins; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; C510164:CYP3A5 protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human