posted on 2012-11-21, 00:00authored byBin Cai, Lowell P. Bush
Nornicotine is the demethylation product of nicotine
and the precursor
of tobacco-specific nitrosamine N′-nitrosonornicotine
(NNN) in tobacco (Nicotiana tabacum L.). There is
an inconsistent enantiomer fraction (EF) of nornicotine reported in
the literature. The objective of this study was to explore possible
mechanisms to account for the variable EFnnic in tobacco.
A survey of tobacco with different demethylating capabilities confirmed
that there was variable EFnnic. Experiments of induction
and inhibition of the major nicotine demethylase CYP82E4 activity
in tobacco demonstrated that CYP82E4 selectively demethylated (S)-nicotine and resulted in different EFnnic in
tobacco leaves. Results from plants with silenced demethylases by
RNAi suggested that other demethylases selectively used (R)-nicotine and resulted in high EFnnic. In summary, enantioselective
demethylation likely plays an important role in contributing to a
large and variable EFnnic observed in tobacco.