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3-Methylcholanthrene-induced Monooxygenase (O-Deethylation) Activity of Human Lymphocytes¹

Biochemistry Department, University of Texas Health Science Center, Dallas, Texas 75235 [M. D. B.]; Veterinary Toxicology and Entomology, Research Laboratory, Agricultural Research Service, United States Department of Agriculture, College Station, Texas 77840 [R. T. M.]; and Department of Biochemical Oncology, Microbiological Associates, Bethesda, Maryland 20014 [R. E. K.]

With a direct fluorescence assay, the levels of mixed-function oxidase activity were determined in mitogen-activated human lymphocytes. The O-deethylation of ethoxyresorufin to resorufin was used to quantitate mixed-function oxidase activity. Ethoxyresorufin O-deethylase activity was low to nondetectable in noninduced, mitogen-activated cells, but it was readily detected in 3-methylcholanthrene, mitogen-activated lymphocytes. The activity was: (a) dependent on assay time and number of lymphocytes; (b) dependent on the presence of reduced nicotinamide adenine dinucleotide phosphate; (c) stable to freezing at -80° for at least 2 weeks; (d) reproducibly detected in duplicate samples of blood from one individual when cultured and assayed at the same time; but (e) quite variable in samples of blood from one individual at different times. Since in hepatic and pulmonary tissue of model animal systems ethoxyresorufin is a specific substrate for cytochrome P-448-associated monooxygenases, the use of this chemical could proffer an assay that specifically measures human cytochrome P-448-associated activity.

¹ This work was supported by National Cancer Institute Contracts N01-CP-33362, N01-CP-43309, and N01-CP-55605 and by contracts from the Council for Tobacco Research. The mention herein of a proprietary product does not constitute an endorsement by the United States Department of Agriculture.

² Present address: Forensic Science Department, Karolinska Institutet, S-10401 Stockholm, Sweden.

Received 1/19/76. Accepted 11/ 9/76.

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