Tricolorin A, a potent natural uncoupler and inhibitor of photosystem II acceptor side of spinach chloroplasts |
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Authors: | Lahoucine Achnine Rogelio Pereda-Miranda Roberto Iglesias-Prieto Rafael Moreno-Sánchez Blas Lotina-Hennsen |
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Institution: | Departamento de Bioquímica, Facultad de Química. Universidad Nacional Autónoma de México (UNAM), México, DF 04510, México; Departamento de Farmacia, Facultad de Química, UNAM, México, DF 04510, México; Estación de Investigaciones Marinas "Puerto Morelos", ICMyL-UNAM. Apartado Postal 1152, Cancún 77500, México; Departamento de Bioquímica, Instituto Nacional de Cardiología, México DF 14080, México |
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Abstract: | Tricolorin A, (11 S )-11-hydroxyhexadecanoic acid 11- O - α - l - rhamnopyranosyl-(1?3)- O - α - l -{2- O -(2 S -methylbutanoyl)-4- O -(2 S -methylbutanoyl)}-rhamnopyranosil-(1?2)- O - β - d -glucopyranosil-(1?2)- β -fucopyranoside-(1,3'-lactone), the major phytogrowth inhibitor isolated from Ipomoea tricolor Cav. (Convolvulaceae) was found to be a potent uncoupler (U50=0.33 μ M ) of photophosphorylation in spinach chloroplasts. Tricolorin A inhibited H+-uptake and adenosine 5'-triphosphate (ATP) synthesis, and stimulated basal and phosphorylating electron flows. Using a combination of two well-known fluorescent ΔpH probes, 9-aminoacridine and 9-amino-6-chloro-2-methoxyacridine, the uncoupling behavior of tricolorin A was also demonstrated for submitochondrial particles. Polarographic data showed that high concentrations (20 μ M ) of tricolorin A inhibited photosystem II (PSII) electron flow at the level of plastoquinone B (QB). Chlorophyll (Chl) a fluorescence analysis showed that tricolorin A induced accumulation of QA? and strongly decreased the electron transport capacity, suggesting that the target of this molecule was located at the QB level. The macrocyclic lactone-type structure of this allelopathic agent proved to be an important structural requirement for uncoupling activity since its hydrolysis caused loss of the inhibitory potential. |
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