title: 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.
abstract: 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.
authors: Departamento de Química, Universidad Federal de Minas Gerais, Avenida Antonio Carlos 6627, Pampulha, 31270-901 Belo Horizonte, MG, Brazil.
authors: Djalma
authors: D
authors: Menezes-de-Oliveira
authors: Maria-Isabel
authors: MI
authors: Aguilar
authors: Beatriz
authors: B
authors: King-Díaz
authors: Sidney Augusto
authors: SA
authors: Vieira-Filho
authors: Lucinier
authors: L
authors: Pains-Duarte
authors: Grácia-Divina de Fátima
authors: GD
authors: Silva
authors: Blas
authors: B
authors: Lotina-Hennsen
mesh_terms: D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D005453:Fluorescence; D004376:Galactitol / Q000737:chemistry / Q000494:pharmacology*; D007700:Kinetics; D008027:Light; D029755:Maytenus / Q000737:chemistry; D010269:Paraquat / Q000378:metabolism; D053978:Pentacyclic Triterpenes / Q000737:chemistry / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D010788:Photosynthesis / Q000187:drug effects* / Q000528:radiation effects*; D018515:Plant Leaves / Q000187:drug effects / Q000528:radiation effects; D018724:Spinacia oleracea / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D020524:Thylakoids / Q000187:drug effects / Q000201:enzymology / Q000528:radiation effects; D014315:Triterpenes / Q000737:chemistry / Q000494:pharmacology*; D000094042:Lupanes
chemical_list: D017301:Ca(2+) Mg(2+)-ATPase; D002734:Chlorophyll; D000077194:Chlorophyll A; D004376:Galactitol; D010269:Paraquat; D053978:Pentacyclic Triterpenes; D014315:Triterpenes; C010480:lupeol; D000094042:Lupanes