Two Tropinone Reductases with Distinct Stereospecificities from Cultured Roots of Hyoscyamus niger
- 1 October 1992
- journal article
- Published by Oxford University Press (OUP) in Plant Physiology
- Vol. 100 (2) , 836-845
- https://doi.org/10.1104/pp.100.2.836
Abstract
Tropinone is an alkamine intermediate at the branch point of biosynthetic pathways leading to various tropane alkaloids. Two stereospecifically distinct NADPH-dependent oxidoreductases, TR-I and TR-II, which, respectively, reduce tropinone to 3alpha-hydroxytropane (tropine) and 3beta-hydroxytropane (psi-tropine), were detected mainly in the root of tropane alkaloid-producing plants but not in nonproducing cultured root. Both reductases were purified to near homogeneity from cultured root of Hyoscyamus niger and characterized. The TR-I reaction was reversible, whereas the TR-II reaction was essentially irreversible, reduction of the ketone being highly favored over oxidation of the alcohol psi-tropine. Marked differences were found between the two reductase in their affinities for tropinone substrate and in the effects of amino acid modification reagents. Some differences in substrate specificity were apparent. For example, N-propyl-4-piperidone was reduced by TR-II but not by TR-I. Conversely, 3-quinuclidinone and 8-thiabicyclo[3,2,1]octane-3-one were accepted as substrates by TR-I but hardly at all by TR-II. Both enzymes were shown to be class B oxidoreductases, which transfer the pro-S hydrogen of NAD(P)H to their substrates. Possible roles of these tropinone reductases in alkaloid biosynthesis are discussed.Keywords
This publication has 9 references indexed in Scilit:
- Stress responses in alfalfa (Medicago sativa L.) 11. Molecular cloning and expression of alfalfa isoflavone reductase, a key enzyme of isoflavonoid phytoalexin biosynthesisPlant Molecular Biology, 1991
- Hyoscyamine 6 beta-hydroxylase, an enzyme involved in tropane alkaloid biosynthesis, is localized at the pericycle of the root.1991
- Recent Developments in the Biosynthesis of the Tropane Alkaloids1Planta Medica, 1990
- Hyoscyamine 6β-Hydroxylase, a 2-Oxoglutarate-Dependent Dioxygenase, in Alkaloid-Producing Root CulturesPlant Physiology, 1986
- Partial Purification and Properties of Tropine Dehydrogenase from Root Cultures ofDatura stramoniumPlanta Medica, 1982
- A Rapid and Sensitive Method for the Quantitation of Microgram Quantities of Protein Utilizing the Principle of Protein-Dye BindingAnalytical Biochemistry, 1976
- Reduction of coenzyme a thioesters of cinnamic acids with an enzyme preparation from lignifying tissue of ForsythiaFEBS Letters, 1975
- Nutrient requirements of suspension cultures of soybean root cellsExperimental Cell Research, 1968
- Statistical estimations in enzyme kineticsBiochemical Journal, 1961