Metabolism of monoterpenes: early steps in the metabolism of d-neomenthyl-. beta. -D-glucoside in peppermint (Mentha piperita) rhizomes
Previous studies have shown that the monoterpene ketone l-(G-/sup 3/H) menthone is reduced to the epimeric alcohols l-menthol and d-neomenthol in leaves of flowering peppermint (Mentha piperita L.), and that a portion of the menthol is converted to methyl acetate while the bulk of the neomenthol is transformed to neomenthyl-..beta..-D-glucoside which is then transported to the rhizome. Analysis of the disposition of l-(G)/sup 3/H)menthone applied to midstem leaves of intact flowering plants allowed the kinetics of synthesis and transport of the monoterpenyl glucoside to be determined, and gave strong indication that the glucoside was subsequently metabolized in the rhizome. Studies with d-(G-/sup 3/H)neomenthyl-..beta..-D-glucoside as substrate, using excised rhizomes or rhizome segments, confirmed the hydrolysis of the glucoside as an early step in metabolism at this site, and revealed that the terpenoid moiety was further converted to a series of ether-soluble, methanol-soluble, and water-soluble products. The conversion of menthone to the lactone, and of the lactone to more polar products, were confirmed in vivo using l-(G-/sup 3/H)menthone and l-(G-/sup 3/H)-3,4-menthone lactone as substrates. Additional oxidation products were formed in vivo via the desaturation of labeled neomenthol and/or menthone, but none of these transformations appeared to lead to ring opening of the p-menthane skeleton. Each step in the main reaction sequence, from hydrolysis of neomenthyl glucoside to lactonization of menthone, was demonstrated in cell-free extracts from the rhizomes of flowering mint plants. The lactomization step is of particular significance in providing a means of cleaving the p-methane ring to afford an acyclic carbon skeleton that can be further degraded by modifications of the well-known ..beta..-oxidation sequence. 41 references, 3 figures, 1 table.
- Research Organization:
- Washington State Univ., Pullman
- DOE Contract Number:
- AM06-76RL02221; AT06-82ER12027
- OSTI ID:
- 6094726
- Journal Information:
- Plant Physiol.; (United States), Journal Name: Plant Physiol.; (United States) Vol. 76:3; ISSN PLPHA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
560303* -- Chemicals Metabolism & Toxicology-- Plants-- (-1987)
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
METABOLISM
ORGANIC COMPOUNDS
PLANTS
TERPENES
TRACER TECHNIQUES
TRITIUM COMPOUNDS