The triterpenes 3β-lup-20(29)-en-3-ol and 3β-lup-20(29)-en-3-yl acetate and the carbohydrate 1,2,3,4,5,6-hexa-O-acetyl-dulcitol as photosynthesis light reactions inhibitors

• Published in: Molecules (Basel, Switzerland) Vol. 16; no. 12; pp. 9939 - 9956
• Main Authors: Menezes-de-Oliveira, Djalma, Aguilar, Maria-Isabel, King-Díaz, Beatriz, Vieira-Filho, Sidney Augusto, Pains-Duarte, Lucinier, Silva, Grácia-Divina de Fátima, Lotina-Hennsen, Blas
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI 01.12.2011; MDPI AG
• Subjects: 1,2,3,4,5,6-hexa-O-acetyldulcitol; 3β-lup-20-en-3-yl acetate; Ca(2+) Mg(2+)-ATPase - metabolism; Chlorophyll - metabolism; Chlorophyll A; chlorophyll a fluorescence; Electron Transport - drug effects; Electron Transport - radiation effects; energy transfer inhibitor; Fluorescence; Galactitol - chemistry; Galactitol - pharmacology; Hill reaction inhibitors; Kinetics; Light; lup-20-en-3β-ol; lupeol; Maytenus - chemistry; Maytenus acanthophylla; Paraquat - metabolism; Pentacyclic Triterpenes - chemistry; Pentacyclic Triterpenes - pharmacology; Phosphorylation - drug effects; Phosphorylation - radiation effects; Photosynthesis - drug effects; Photosynthesis - radiation effects; Plant Leaves - drug effects; Plant Leaves - radiation effects; Spinacia oleracea - drug effects; Spinacia oleracea - metabolism; Spinacia oleracea - radiation effects; Thylakoids - drug effects; Thylakoids - enzymology; Thylakoids - radiation effects; Triterpenes - chemistry; Triterpenes - pharmacology; uncoupler; Xylosma flexuosa
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules16129939

Three compounds were isolated from Maytenus acanthophylla Reissek (Celastraceae): the pentacyclic triterpenes lup-20(29)-en-3β-ol (lupeol, 1) and 3β-lup-20(29)-en-3-yl acetate (2) and the carbohydrate 1,2,3,4,5,6-hexa-O-acetyldulcitol (3); lupeol was also isolated from Xylosma flexuosa. The compounds' structures were elucidated by spectroscopic and spectrometric analysis. Compound 1 acts as an energy transfer inhibitor, interacting with isolated CF₁ bound to thylakoid membrane, and dulcitol hexaacetate 3 behaves as a Hill reaction inhibitor and as an uncoupler, as determined by polarography. Chlorophyll a (Chl a) fluorescence induction kinetics from the minimum yield F₀ to the maximum yield F(M )provides information of the filling up from electrons coming from water to plastoquinone pool with reducing equivalents. In this paper we have examined the effects of compounds 1 and 3 on spinach leaf discs. Compound 1 induces the appearance of a K-band, which indicates that it inhibits the water splitting enzyme. In vivo assays measuring the fluorescence of chl a in P. ixocarpa leaves sprayed with compound 1, showed the appearance of the K-band and the PSII reaction centers was transformed to "heat sinks" or silent reaction centers unable to reduce Q(A). However, 3 also induced the appearance of a K band and a new band I appears in P. ixocarpa plants, therefore it inhibits at the water splitting enzyme complex and at the PQH₂ site on b₆f complex. Compounds 1 and 3 did not affect chlorophyll a fluorescence of L. perenne plants.