Dimethylnitrosamine-demethylase: Absence of increased enzyme catabolism and multiplicity of effector sites in repression. Hemoprotein involvement

Argus, Mary P.; Arcos, Joseph C.; Pastor, Karen M.; Wu, Benjamin C.; Venkatesan, Natarajan

doi:10.1016/0009-2797(76)90002-8

Cited by 39 publications

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“…25, 26, 52, 53 In many earlier studies relatively high concentrations of DMN were used, but P450 enzymes in what is now known as Subfamily 2B were active. 25, 26 We selected (rat) P450 2B1, which had been studied before (then termed “P450 PB-B”).…”

Section: Resultsmentioning

confidence: 99%

“…Although P450 2E1 and 2A6 appear to be the enzymes most involved in the oxidations of small alkyl nitrosamines, − ,, other P450s can oxidize nitrosamines to aldehydes, including DMN. ,,, In many earlier studies, relatively high concentrations of DMN were used, but P450 enzymes in what is now known as subfamily 2B were active. , We selected (rat) P450 2B1, which had been studied before (then termed “P450 PB-B”). , …”

Section: Resultsmentioning

confidence: 99%

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Oxidation of Methyl and Ethyl Nitrosamines by Cytochrome P450 2E1 and 2B1

et al. 2012

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Cytochrome P450 (P450) 2E1 is the major enzyme that oxidizes N-nitrosodimethylamine (N,N-dimethylnitrosamine, DMN), a carcinogen and also a representative of some nitrosamines formed endogenously. Oxidation of DMN by rat or human P450 2E1 to HCHO showed a high apparent intrinsic kinetic deuterium isotope effect (KIE), ≥ 8. The KIE was not attenuated in non-competitive intermolecular experiments with rat liver microsomes (DV 12.5, D(V/K) 10.9, nomenclature of Northrop, D.B. (1982) Methods Enzymol. 87, 607–625) but was with purified human P450 2E1 (DV 3.3, D(V/K) 3.7), indicating that C-H bond breaking is partially rate-limiting with human P450 2E1. With N-nitrosodiethylamine (N,N-diethylnitrosamine, DEN), the intrinsic KIE was slightly lower and was not expressed (e.g., D(V/K) 1.2) in non-competitive intermolecular experiments. The same general pattern of KIEs was also seen in the D(V/K) results with DMN and DEN for the minor products resulting from the denitrosation reactions (CH3NH2, CH3CH2NH2, and NO2−). Experiments with deuterated N-nitroso-N-methyl,N-ethylamine demonstrated that the lower KIEs associated for ethyl compared to methyl oxidation could be distinguished within a single molecule. P450 2E1 oxidized DMN and DEN to aldehydes and then to the carboxylic acids. No kinetic lags were observed in acid formation; pulse-chase experiments with carrier aldehydes showed only limited equilibration with P450 2E1-bound aldehydes, indicative of processive reactions, as reported for P450 2A6 (Chowdhury, G. et al. (2010) J. Biol. Chem. 285, 8031–8044). These same features (no lag phase for HCO2H formation, lack of equilibration in pulse-chase assays) were also seen with (rat) P450 2B1, which has lower catalytic efficiency for DMN oxidation and a larger active site. Thus, the processivity of dialkylnitrosamine oxidation appears to be shared by a number of P450s.

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