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 3α-hydroxytropane (tropine) and 3β-hydroxytropane (ψ-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 ψ-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.
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- Bradford M. M. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976 May 7;72:248–254. doi: 10.1016/0003-2697(76)90527-3. [DOI] [PubMed] [Google Scholar]
- Gamborg O. L., Miller R. A., Ojima K. Nutrient requirements of suspension cultures of soybean root cells. Exp Cell Res. 1968 Apr;50(1):151–158. doi: 10.1016/0014-4827(68)90403-5. [DOI] [PubMed] [Google Scholar]
- Gross G. G., Kreiten W. Reduction of coenzyme A thioesters of cinnamic acids with an enzyme preparation from lignifying tissue of Forsythia. FEBS Lett. 1975 Jun 15;54(2):259–262. doi: 10.1016/0014-5793(75)80087-1. [DOI] [PubMed] [Google Scholar]
- Hashimoto T., Hayashi A., Amano Y., Kohno J., Iwanari H., Usuda S., Yamada Y. Hyoscyamine 6 beta-hydroxylase, an enzyme involved in tropane alkaloid biosynthesis, is localized at the pericycle of the root. J Biol Chem. 1991 Mar 5;266(7):4648–4653. [PubMed] [Google Scholar]
- Hashimoto T., Yamada Y. Hyoscyamine 6beta-hydroxylase, a 2-oxoglutarate-dependent dioxygenase, in alkaloid-producing root cultures. Plant Physiol. 1986 Jun;81(2):619–625. doi: 10.1104/pp.81.2.619. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Koelen K. J., Gross G. G. Partial purification and properties of tropine dehydrogenase from root cultures of Datura stramonium. Planta Med. 1982 Apr;44(4):227–230. doi: 10.1055/s-2007-971454. [DOI] [PubMed] [Google Scholar]
- Leete E. Recent developments in the biosynthesis of the tropane alkaloids. Planta Med. 1990 Aug;56(4):339–352. doi: 10.1055/s-2006-960979. [DOI] [PubMed] [Google Scholar]
- Paiva N. L., Edwards R., Sun Y. J., Hrazdina G., Dixon R. A. Stress responses in alfalfa (Medicago sativa L.) 11. Molecular cloning and expression of alfalfa isoflavone reductase, a key enzyme of isoflavonoid phytoalexin biosynthesis. Plant Mol Biol. 1991 Oct;17(4):653–667. doi: 10.1007/BF00037051. [DOI] [PubMed] [Google Scholar]
- WILKINSON G. N. Statistical estimations in enzyme kinetics. Biochem J. 1961 Aug;80:324–332. doi: 10.1042/bj0800324. [DOI] [PMC free article] [PubMed] [Google Scholar]