( )-Menthofuran is an undesirable monoterpenoid component of peppermint (Mentha x piperita) essential oil that is derived from the ,-unsaturated ketone ( )-pulegone. Microsomal preparations, from the oil gland secretory cells of a high ( )-menthofuran-producing chemotype of Mentha pulegium, transform ( )-pulegone to ( )-menthofuran in the presence of NADPH and molecular oxygen, implying that menthofuran is synthesized by a mechanism analogous to that of mammalian liver cytochrome P450s involving the hydroxylation of the syn-methyl group of ( )-pulegone, spontaneous intramolecular cyclization to the hemiketal, and dehydration to the furan. An abundant cytochrome P450 clone from a peppermint oil gland cell cDNA library was functionally expressed in Saccharomyces cerevisiae and Escherichia coli and shown to encode the ( )-menthofuran synthase (i.e., ( )-pulegone-9-hydroxylase). The full-length cDNA contains 1479 nucleotides, and encodes a protein of 493 amino acid residues of molecular weight 55,360, which bears all of the anticipated primary structural elements of a cytochrome P450 and most closely resembles (35% identity) a cytochrome P450 monoterpene hydroxylase, ( )-limonene-3-hydroxylase, from the same source. The availability of this gene permits transgenic manipulation of peppermint to improve the quality of the derived essential oil.
Bertea, C. M., Schalk, M., Karp, F., Maffei, M., & Croteau, R. (2001). Demonstration that menthofuran synthase of mint (Mentha) is a cytochrome P450 monooxygenase: cloning, functional expression, and characterization of the responsible gene. Archives of Biochemistry and Biophysics, 390, 279-286. https://doi.org/10.1006/abbi.2001.2378