High Quality Content by WIKIPEDIA articles! Nicotine-derived nitrosamine ketone (NNK), or 4-(methylnitrosamino)- 1-(3-pyridyl)-1-butanone, is a nitrosamine present in tobacco that is a potent procarcinogen. It is activated by CYP2A6. It is a biomarker of exposure to cigarette smoke. It is produced upon the curing of tobacco.