Metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific carcinogen, by rabbit nasal microsomes and cytochrome P450s NMa and NMb.
Rabbit nasal olfactory and respiratory microsomes were found to catalyze the alpha-hydroxylation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) with specific activities of 262 and 136 pmol/min/mg protein in the formation of keto aldehyde, and of 318 and 190 pmol/min/mg protein in the formation of keto alcohol respectively. The formation of NNK-N-oxide was observed in experiments with rabbit olfactory and respiratory microsomes, but not with rat nasal microsomes. However, the rat nasal microsomes had higher activity in catalyzing the alpha-hydroxylation of NNK. In a reconstituted system, rabbit P450NMa, a major constitutive P450 isozyme in nasal microsomes, displayed high activities in the formation of the keto aldehyde and the keto alcohol with apparent Km values of 15 and 9 microM respectively. In comparison, rabbit olfactory specific P450NMb had a low activity in catalyzing the formation of keto aldehyde (Km = 186 microM) and no activity in the formation of keto alcohol. The P450NMa-catalyzed oxidation of NNK was inhibited by nicotine and diallyl sulfide. Kinetic studies indicated that nicotine is a competitive inhibitor. These results demonstrate that enzymes in rabbit nasal microsomes, especially P450NMa, efficiently catalyze the bioactivation of NNK.
Hong
J Y
JY
Laboratory for Cancer Research, Rutgers University, Piscataway, NJ 08855.
Ding
X
X
Smith
T J
TJ
Coon
M J
MJ
Yang
C S
CS
D000818:Animals; D002273:Carcinogens / Q000378:metabolism* / Q000633:toxicity; D002384:Catalysis; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D006900:Hydroxylation; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008861:Microsomes / Q000378:metabolism*; D009297:Nasal Mucosa / Q000378:metabolism*; D009602:Nitrosamines / Q000378:metabolism* / Q000633:toxicity; D010947:Plants, Toxic; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D014026:Nicotiana / Q000737:chemistry
D002273:Carcinogens; D007527:Isoenzymes; D009602:Nitrosamines; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; D003577:Cytochrome P-450 Enzyme System