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Biomedical subjects

R T Mayer

Publications and source records attributed to R T Mayer.

50 records · Page 3Linked to original sources
PubMed1977

3-methylcholanthrene-induced monooxygenase (O-deethylation) activity of human lymphocytes.

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 degrees 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.

Adult↗
PubMedDate not supplied

Characteristics of a microsomal cytochrome P-448-mediated reaction. Ethoxyresorufin O-de-ethylation.

Certain characteristics of ethoxyresorufin O-de-ethylation, as catalyzed by microsomes of liver, lung, and intestine of control and pretreated rats and hamsters, were studied. The results support previous suggestions that the reaction is catalyzed primarily by a 3-methyl-cholanthrene (MC)-inducible mono-oxygenase which has a 448-nm absorption maximum in the reduced-CO difference spectrum. Ethoxyresorufin exhibited a type I binding spectrum with liver microsomes from MC-induced rats, but there was no clear interaction with microsomes from control or phenobarbital (PB)-induced rats. Maximum MC-induction of type I binding and de-ethylase activity coincided with the appearance of a cytochrome P-450 spectrum whose absorption maximum was shifted to 448 nm. Low concentrations of alpha-naphthoflavone (ANF) or benzo[a]pyrene (BP) inhibited the de-ethylation with liver microsomes of MC-treated rats (150 approximately 10(-9)M) but not those of control rats. A kinetic analysis of BP inhibition of this reaction showed it to be competitive. Inhibition of the MC-induced liver microsomal reaction by low concentrations of BP or ANF diminished rapidly with time. MC-induced rat liver microsomal de-ethylation of ethoxyresorufin was less sensitive than the PB-induced reaction to inhibition by metyrapone or SKF 525-A (I50 approximately 10(-6) - 10(-4)M). However, microsomes from rat liver, lung, and intestine had very low constitutive activities (less than 0.1 nmol/min/mg of protein). MC greatly induced the de-ethylation reaction in liver (200 X), intestine (40 X) and lung (10 X). De-ethylation of ethoxyresorufin in microsomes from control and MC-induced rat lung was inhibited by low concentrations of either ANF or BP (I50 approximately 10(-8) M). Control hamster liver microsomes were several times more active in de-ethylation than control rat liver microsomes, but MC-induction of hamster liver was only 1/10 of that in rat liver. Control hamster lung activity was similar to that of control rat lung, but was not appreciably induced by MC.

Animals↗
PubMedDate not supplied

Inherent specificities of purified cytochromes P-450 and P-448 toward biphenyl hydroxylation and ethoxyresorufin deethylation.

Liver microsomes from 3-methylcholanthrene-pretreated Long-Evans rats catalyzed the 2- and the 4-hydroxylation of biphenyl and the O-deethylation of ethoxyresorufin, sustained by either NADPH or cumene hydroperoxide. In contrast, the liver microsomes from corn oil- or phenobarbital-pretreated rats catalyzed the NADPH- or cumene hydroperoxide-sustained 4-hydroxylation of biphenyl, but the rates of 2-hydroxylation or ethoxyresorufin deethylation were negligible. A monooxygenase system reconstituted with partially purified NADPH-cytochrome c reductase and cytochrome P-448 catalyzed NADPH-supported biphenyl 2- and 4-hydroxylation and ethoxyresorufin deethylation. A monooxygenase system reconstituted with the reductase and cytochrome P-450 catalyzed NADPH-supported biphenyl 4-hydroxylation but exhibited negligible 2-hydroxylation or ethoxyresorufin deethylation activites. Solubilized cytochrome P-448 catalyzed biphenyl 2- and 4-hydroxylation and ethoxyresorufin deethylation sustained by cumene hydroperoxide in the absence of both NADPH and NADPH-cytochrome c reductase, whereas solubilized cytochrome P-450, under the same conditions, catalyzed only biphenyl 4-hydroxylation. It is concluded that the patterns of biphenyl hydroxylation and ethoxyresorufin deethylation observed with live- microsomes from untreated or inducer-treated rats are due largely to the inherent enzymic specificities of their cytochromes P-450 and P-448.

Animals↗