Characterization of binding of N'-nitrosonornicotine to protein
The NADPH-dependent activation of the carcinogenic nitrosamine, N'-nitrosonornicotine (NNN) to a reactive intermediate which binds covalently to protein was assessed using male Sprague-Dawley rat liver and lung microsomes. The NADPH-dependent covalent binding of (/sup 14/C)NNN to liver and lung microsomes was linear with time up to 90 and 45 min, respectively and was also linear with protein concentrations up to 3.0 and 2.0 mg/ml, respectively. The apparent K/sub m/ and V/sub max/ of the NADPH-dependent binding to liver microsomes were determined from the initial velocities. Addition of the thiols glutathione, cystein, N-acetylcysteine or 2-mercapthoethanol significantly decreased the non-NADPH-dependent binding to liver microsomal protein, but did not affect the NADPH-dependent binding. Glutathione was required in order to observe any NADPH-dependent binding to lung microsomal protein. In lung microsomes, SKF-525A significantly decreased the NADPH-dependent binding by 79%. Replacement of an air atmosphere with N/sub 2/ or CO:O/sub 2/ (8:2) significantly decreased the NADPH-dependent binding of (/sup 14/C)NNN to liver microsomal protein by 40% or 27% respectively. Extensive covalent binding of (/sup 14/C)NNN to liver and muscle microsomal protein occurred in the absence of an NADPH-generating system, in the presence of 50% methanol and also to bovine serum albumin, indicating a nonenzymatic reaction. These data indicate that cytochrome P-450 is at least in part responsible for the metabolic activation of the carcinogen NNN, but also suggest additional mechanisms of activation.
- Research Organization:
- Kentucky Univ., Lexington (USA)
- OSTI ID:
- 6713093
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
AMINES
ANIMALS
BIOCHEMICAL REACTION KINETICS
BIOCHEMISTRY
BODY
CARBON 14 COMPOUNDS
CELL CONSTITUENTS
CHEMISTRY
COENZYMES
CONFIGURATION INTERACTION
DIGESTIVE SYSTEM
GLANDS
KINETICS
LABELLED COMPOUNDS
LIVER
LUNGS
MAMMALS
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MICROSOMES
MUSCLES
NADP
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NITROSO COMPOUNDS
NUCLEOTIDES
ORGANIC COMPOUNDS
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ORGANOIDS
ORGANS
PROTEINS
RATS
REACTION KINETICS
RESPIRATORY SYSTEM
RODENTS
VERTEBRATES