Effect of birch bark dry extract on the key biotransformation enzymes (cytochrome P-450) and microsomal membranes in rat liver

We have developed a specific radioimmunoassay to quantify NADPH: cytochrome P-450 reductase. The assay is based on the use of 125I-labelled NADPH: cytochrome P-450 reductase as the radiolabelled antigen and can detect quantities of this protein in amounts as low as 30 pg. The results of the radioimmunoassay demonstrates that the 2.7-fold increase in enzyme activity in rat liver microsomal membranes after phenobarbital treatment is due to increased amounts of the protein. beta-Naphthoflavone treatment, however, did not alter the activity or the quantity of this enzyme in microsomes. The quantification of NADPH: cytochrome P-450 reductase in the microsomes isolated from control and phenobarbital- and beta-naphthoflavone-treated animals permits the calculation of the ratio of this protein to that of total cytochromes P-450. A molar ratio of 15:1 (cytochromes P-450/NADPH: cytochrome P-450 reductase) was calculated for control and phenobarbital-treated animals. This ratio increased to 21:1 after beta-naphthoflavone treatment. Thus the molar ratio of these proteins in liver microsomes can vary with exposure of the animals to particular xenobiotics.

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Effects of Age, Inducing Agents and Carcinogens on the Distribution of Cytochrome P-450 in Microsomal Membranes from Rat Liver

Biochemical Society Transactions ◽

10.1042/bst0060959a ◽

1978 ◽

Vol 6 (5) ◽

pp. 959-961

Author(s):

T. W. POOLE ◽

D. V. PARKE

Keyword(s):

Rat Liver ◽

Microsomal Membranes ◽

Cytochrome P 450

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Induction and repression of the major phenobarbital-induced cytochrome P-450 measured by radioimmunoassay

Biochemical Journal ◽

10.1042/bj2120055 ◽

1983 ◽

Vol 212 (1) ◽

pp. 55-64 ◽

Cited By ~ 32

Author(s):

I R Phillips ◽

E A Shephard ◽

R M Bayney ◽

S F Pike ◽

B R Rabin ◽

...

Keyword(s):

Rat Liver ◽

Total Content ◽

Fold Increase ◽

Differential Effects ◽

Microsomal Membranes ◽

Fold Induction ◽

Purified Antigen ◽

Cytochrome P 450

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.

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