NADH cannot replace NADPH as reductant. The Delta8,9-double bond of (+)-cis-isopulegone and the Delta1,2-double bond of (+/-)-piperitone are not substrates. The enzyme from peppermint (Mentha x piperita) converts (+)-pulegone into both (-)-menthone and (+)-isomenthone at a ratio of 70:30 for native enzyme but it does not catalyse the reverse reaction. This enzyme is a member of the medium-chain dehydrogenase/reductase superfamily.
Ringer KL, McConkey ME, Davis EM, Rushing GW, Croteau R
Title
Monoterpene double-bond reductases of the (-)-menthol biosynthetic pathway: isolation and characterization of cDNAs encoding (-)-isopiperitenone reductase and (+)-pulegone reductase of peppermint.
