Publications

• Metabolism of monoterpenes: demonstration that (+)-cis-isopulegone, not piperitenone, is the key intermediate in the conversion of (-)-isopiperitenone to (+)-pulegone in peppermint (Mentha piperita).

  Croteau R., Venkatachalam K.V.

  Piperitenone is commonly considered to be the key intermediate in the conversion of (-)-isopiperitenone to (+)-pulegone in peppermint; however, [3H]piperitenone gave rise only to the inert metabolite (+)-piperitone when incubated with peppermint leaf discs. Under identical conditions, (-)-[3H]isop ... >> More

  Piperitenone is commonly considered to be the key intermediate in the conversion of (-)-isopiperitenone to (+)-pulegone in peppermint; however, [3H]piperitenone gave rise only to the inert metabolite (+)-piperitone when incubated with peppermint leaf discs. Under identical conditions, (-)-[3H]isopiperitenone was efficiently incorporated into (+)-pulegone, (-)-menthone, and (+)-isomenthone in leaf discs, and yielded an additional metabolite identified as (+)-cis-isopulegone; piperitenone was poorly labeled. Moreover, (+)-cis-[3H]isopulegone was rapidly converted to (+)-pulegone, (-)-menthone, and (+)-isomenthone in leaf discs, and the reduction of (+)-[3H]pulegone to (-)-menthone and (+)-isomenthone was similarly documented. Each step of the pathway was demonstrated in a crude soluble preparation from peppermint leaf epidermis and each of the relevant enzymes was partially purified in order to compare relative rates of catalysis. The results of these studies indicate that the endocyclic double bond of (-)-isopiperitenone is reduced to yield (+)-cis-isopulegone, which is isomerized to (+)-pulegone as the immediate precursor of (-)-menthone and (+)-isomenthone, and they rule out piperitenone as an intermediate of the pathway. << Less

  Arch Biochem Biophys 249:306-315(1986) [PubMed] [EuropePMC]

• Monoterpene double-bond reductases of the (-)-menthol biosynthetic pathway: isolation and characterization of cDNAs encoding (-)-isopiperitenone reductase and (+)-pulegone reductase of peppermint.

  Ringer K.L., McConkey M.E., Davis E.M., Rushing G.W., Croteau R.

  Random sequencing of a peppermint essential oil gland secretory cell cDNA library revealed a large number of clones that specified redox-type enzymes. Full-length acquisitions of each type were screened by functional expression in Escherichia coli using a newly developed in situ assay. cDNA clones ... >> More

  Random sequencing of a peppermint essential oil gland secretory cell cDNA library revealed a large number of clones that specified redox-type enzymes. Full-length acquisitions of each type were screened by functional expression in Escherichia coli using a newly developed in situ assay. cDNA clones encoding the monoterpene double-bond reductases (-)-isopiperitenone reductase and (+)-pulegone reductase were isolated, representing two central steps in the biosynthesis of (-)-menthol, the principal component of peppermint essential oil, and the first reductase genes of terpenoid metabolism to be described. The (-)-isopiperitenone reductase cDNA has an open reading frame of 942 nucleotides that encodes a 314 residue protein with a calculated molecular weight of 34,409. The recombinant reductase has an optimum pH of 5.5, and K(m) values of 1.0 and 2.2 microM for (-)-isopiperitenone and NADPH, respectively, with k(cat) of 1.3s(-1) for the formation of the product (+)-cis-isopulegone. The (+)-pulegone reductase cDNA has an open reading frame of 1026 nucleotides and encodes a 342 residue protein with a calculated molecular weight of 37,914. This recombinant reductase catalyzes the reduction of the 4(8)-double bond of (+)-pulegone to produce both (-)-menthone and (+)-isomenthone in a 55:45 ratio, has an optimum pH of 5.0, and K(m) values of 2.3 and 6.9 microM for (+)-pulegone and NADPH, respectively, with k(cat) of 1.8s(-1). Deduced sequence comparison revealed that these two highly substrate specific double-bond reductases show less than 12% identity. (-)-Isopiperitenone reductase is a member of the short-chain dehydrogenase/reductase superfamily and (+)-pulegone reductase is a member of the medium-chain dehydrogenase/reductase superfamily, implying very different evolutionary origins in spite of the similarity in substrates utilized and reactions catalyzed. << Less

  Arch. Biochem. Biophys. 418:80-92(2003) [PubMed] [EuropePMC]

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