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.
Footnotes
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H.F.P. and Z.E.B. were supported by Simcyp Ltd., Sheffield, UK, and EU Framework 6 (BIOSIM).
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doi:10.1124/dmd.107.015743.
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ABBREVIATIONS: P450, cytochrome P450; rhP450, recombinant human cytochrome P450; HLMSTD, human liver microsomal standard; WX̄, weighted mean; HMG, homogeneity number; VWX̄, variance of the weighted mean.
- Received March 9, 2007.
- Accepted June 25, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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