Two independent radioimmunoassay techniques for the major phenobarbital-inducible cytochrome P-450 (PB P-450) of rat liver microsomal membranes are described. The first technique employs as the source of radiolabelled antigen the products of translation in vitro labelled with [35S]methionine. The second technique employs purified antigen labelled with 125I and is quicker, less expensive and more precise. Both assays are highly specific for PB P-450 and can detect quantities of this variant as small as 1 ng. This is several orders of magnitude more sensitive than any method described previously for the quantification of cytochromes P-450, and consequently the technique is particularly well suited for the quantification of so-called constitutive cytochrome P-450 variants that are present in very low amounts. The results of the radioimmunoassays demonstrate that the apparent 2.6-fold induction of total cytochromes P-450 after phenobarbital treatment is due to a 43-fold increase in Pb P-450. Although β-naphthoflavone increases the total content of cytochrome P-450 of microsomal membranes 1.4-fold, it actually causes a 55% decrease in the amount of PB P-450. Thus different xenobiotics can have differential effects on the expression of the genes for specific cytochrome P-450 variants.
Induction and repression of the major phenobarbital-induced cytochrome P-450 measured by radioimmunoassay
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I R Phillips, E A Shephard, R M Bayney, S F Pike, B R Rabin, R Heath, N Carter; Induction and repression of the major phenobarbital-induced cytochrome P-450 measured by radioimmunoassay. Biochem J 15 April 1983; 212 (1): 55–64. doi: https://doi.org/10.1042/bj2120055
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