title: A diterpene gamma-lactone derivative from Pterodon polygalaeflorus Benth. as a photosystem II inhibitor and uncoupler of photosynthesis.
abstract: 6alpha,7beta-Dihydroxyvouacapan-17beta-oic acid (1) was isolated from Pterodon polygalaeflorus Benth. Modification of 1 yielded 6alpha-hydroxyvouacapan-7beta,17beta-lactone (2) and then 6-oxovouacapan-7beta,17beta-lactone (3). Photosynthesis inhibition by 3 was evaluated in spinach chloroplasts. The uncoupled non-cyclic electron transport rate and ATP synthesis were inhibited by 3, which behaved as a Hill reaction inhibitor. Furthermore, 3 acted as an uncoupler because it enhanced the basal and phosphorylating electron transport rate on thylakoids. This last property of 3 was corroborated when it was observed that it enhances the Mg2+-ATPase activity. In contrast, 3 did not affect photosystem I (PSI) activity. Analysis of the partial photosystem II (PSII) reactions from water to DCPIPOX and water to silicomolybdate allowed to locate the inhibition sites at the redox components of PSII. The OJIP test of the chlorophyll a fluorescence transient confirmed that the inhibition sites were 1.) the oxygen-evolving complex (OEC) and 2.) by the formation of silent centers in the non-QA reducing centers.
authors.affiliation: Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de Mexico, Ciudad Universitaria.
authors.forename: Beatriz
authors.initials: B
authors.lastname: King-Díaz
authors.forename: Flávio J L
authors.initials: FJ
authors.lastname: dos Santos
authors.forename: Mayura M M
authors.initials: MM
authors.lastname: Rubinger
authors.forename: Dorila
authors.initials: D
authors.lastname: Piló-Veloso
authors.forename: Blas
authors.initials: B
authors.lastname: Lotina-Hennsen
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000737:chemistry / Q000378:metabolism; D004224:Diterpenes / Q000302:isolation & purification / Q000378:metabolism*; D007887:Fabaceae / Q000737:chemistry* / Q000502:physiology; D007783:Lactones / Q000302:isolation & purification / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000037:antagonists & inhibitors*; D014475:Uncoupling Agents / Q000302:isolation & purification
chemical_list: D004224:Diterpenes; D007783:Lactones; D045332:Photosystem II Protein Complex; D014475:Uncoupling Agents; D002734:Chlorophyll; D000255:Adenosine Triphosphate