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At least 19 recordsLinked to original sources
PubMed1992

Strictosidine synthase from Rauvolfia serpentina: analysis of a gene involved in indole alkaloid biosynthesis.

The gene for strictosidine synthase (str1), the enzyme which catalyzes the stereospecific condensation of tryptamine and secologanin to form the key indole alkaloid 3 alpha(S)-strictosidine has been isolated from genomic libraries prepared from Rauvolfia serpentina (India) and from Rauvolfia mannii (West Africa). The gene, str1, contained no introns and showed 100% nucleotide sequence homology over 1180 bp, encompassing the entire reading frame, between the two species. Transcription of the R. serpentina gene was found to start 81 nucleotides upstream from the AUG (26 nucleotides downstream from the TATA box). Transient expression assays in Nicotiana plumbaginifolia protoplasts of the R. serpentina str1 5'-noncoding region fused to the beta-glucuronidase reporter gene revealed promoter activity equivalent to 4 +/- 2% of that of 35 S CaMV promoter control. A series of truncated segments of the str1 promoter region indicated the presence of three areas of slight, but reproducible, negative control. Gel retardation assays demonstrated that several regions of the 5'-flanking sequences specifically bound nuclear protein from R. serpentina and that at least one region does not bind R. mannii nuclear protein. A survey of the expression of str1 in the R. serpentina plant suggested that strictosidine synthase poly(A)+ RNA was present predominantly, but not exclusively, in the root. This result correlated well with the distribution of both enzyme activity and indole alkaloids which were also predominant in the root, but, in general, distributed throughout the shrub.

Amino Acid Sequence↗
PubMed2005

[Cytochrome P450 enzymes in biosyntheses of some plant secondary metabolites].

Secologanin, a secoiridoid glucoside, is a pivotal terpenoid intermediate in the biosynthesis of biologically active monoterpenoid indole alkaloids such as reserpine, ajmaline, and vinblastine which are biosynthesized via strictosidine, an alkaloidal glucoside, formed from secologanin and tryptamine. In secologanin biosynthesis, the oxidative cleavage process of loganin to secologanin and the hydroxylation of 7-deoxyloganin to loganin have remained unknown enzymologically and mechanistically. Cornoside is a unique glucoside with 4-hydroxy-2,5-cyclohexadien-1-one (benzoquinol) ring and is widespread in families such as Cornaceae, Oleaceae, and Scrophulariaceae but its biosynthesis, especially the oxidative process, remain to be investigated. Shikonin is a red naphthazarin pigment derived from the roots of Lithospermum erythorhizon and produced biotechnologically by cell cultures. Its biosynthesis including the production regulation mechanism has been investigated in detail. However, the naphthazarin ring formation process, probably starting with the hydroxylation of the side chain of geranylhydroquinone, a key intermediate at the late stage of shikonin biosynthesis, remained unknown. In the present review, cytochrome P450 monooxygenases involved in the biosyntheses of three structurally and biosynthetically interesting compounds, secologanin, cornoside, and shikonin, a described together with the results of previous and recent biosynthetic studies. The biosyntheses of related compounds are also discussed.

Cyclohexanones↗
PubMed1996

Enzymology of indole alkaloid biosynthesis in Catharanthus roseus.

Indole alkaloids in Catharanthus roseus have been in focus because of their medicinal value. These alkaloids consist of an indole moiety provided by tryptamine and a terpenoid portion provided by the secologanin. The most important catharanthus alkaloids are vinblastine (VLB), vincristine (VCR) and ajmalicine. VLB and VCR are clinically useful anticancer agents whereas ajmalicine is used for the treatment of circulatory diseases. VCR and VLB are the most expensive because of their low abundance in the plant, and are formed by the coupling of monomeric indole alkaloids vindoline and catharanthine, catalysed by peroxidases. The pathway that lead to monomeric indole alkaloids involves more than 20 enzymes of which 16 enzymes have been isolated and characterized biochemically, and only three at the molecular level. The present state of knowledge on enzymes and genes involved in indole alkaloid biosynthesis and various aspects of their regulation has been discussed.

Alkaloids↗
PubMed1991

[Effects of verticillatine on cerebral blood flow, cerebral vascular resistance and blood pressure in anesthetized dogs and cats].

The effects of verticillatine (Ver), hexamethonium (Hex) and nimodipine (Nim) on mean arterial pressure (MAP), cerebral blood flow (CBF) and cerebrovascular resistance (CVR) were determined in pentobarbital anesthetized animals using the method of electromagnetic flow meter in dogs and hydrogen clearance in cats. Ver or Nim iv induced significant reduction of MAP and CVR. CBF was increased in dogs and unaltered in cats. The Hex treated dogs and cats exhibited a fall of MAP and CBF with enhancement of CVR. In cats after middle cerebral artery occlusion (MCAO), regional cerebral blood flow (rCBF) was reduced from 190 +/- 70 to 90 +/- 20 ml.kg-1.min-1. Ver and Nim iv caused similar changes of MAP and CVR to those before MCAO. The results suggest that Ver and Nim may have vasodilation effect and improve the cerebral circulation. Thus, they would be beneficial to patients suffering from hypertension.

Animals↗
PubMed2002

Vomilenine reductase--a novel enzyme catalyzing a crucial step in the biosynthesis of the therapeutically applied antiarrhythmic alkaloid ajmaline.

Delineation of the biochemical pathway leading to the antiarrhythmic Rauvolfia alkaloid ajmaline has been an important target in biosynthetic research for many years. The biosynthetic sequence starting with tryptamine and the monoterpene secologanin consists of about 10 different steps. Most of the participating enzymes have been detected and characterized previously, except those catalyzing the reduction of the intermediate vomilenine. A novel NADPH-dependent enzyme that reduces the intermediate has been isolated from Rauvolfia serpentina cell suspension cultures. Vomilenine reductase (M(r )43 kDa, temp opt 30 degrees C, pH opt 5.7-6.2), saturates the indolenine double bond of vomilenine with stereospecific formation of 2beta(R)-1,2-dihydrovomilenine. The described detection, enrichment and properties of the reductase not only closes a gap in ajmaline biosynthesis but is also a prerequisite for overexpressing the protein heterologously for final clarification of its molecular properties.

Ajmaline↗