Mar 10, 1982

Purification and characterization of two constitutive forms of rat liver microsomal cytochrome P-450

The Journal of Biological Chemistry
K C Cheng, J B Schenkman

Abstract

Two constitutive forms of cytochrome P-450 isozymes, designated RLM3 and RLM5, have been purified from untreated rat liver microsomes. RLM3 and RLM5 have minimum molecular weights of 50,000 and 51,000, respectively, based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Absolute oxidized spectra indicate that RLM3 is essentially all in the low spin state, whereas RLM5 contains some high spin component. The CO-reduced difference spectral maximum of RLM3 is at 449 nm and RLM5 is at 451 nm. RLM3 preferentially hydroxylates testosterone at 6 beta and 7 alpha positions and forms an even higher amount of an as yet unidentified polar metabolite, whereas RLM5 hydroxylates testosterone preferentially at 2 beta and 16 alpha positions, and exhibits 6 beta-hydroxylase activity similar to RLM3. RLM5 metabolizes aminopyrine, ethylmorphine, and benzphetamine all faster than does RLM3. When RLM3 and RLM5 were digested with proteolytic enzymes, peptide maps showed that these two cytochrome P-450 isozymes have different primary structures. Cyanogen bromide digestion breaks both isozymes into fragments too small to compare on polyacrylamide gels. Amino acid analyses indicate that RLM3 and RLM5 have very similar but not identical comp...Continue Reading

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Mentioned in this Paper

Testosterone Measurement
Derivatives
Polyacrylamide Gels
Enzymes, antithrombotic
SDS-PAGE
Cytochrome P450
Peptide Hydrolases
Prolylvaline
Proteolytic enzymes for treatment of wounds and ulcers
Ethylmorphine

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