title: 5-O-β-D-galactopyranosyl-7-methoxy-3',4'-dihydroxy-4-phenylcoumarin, an inhibitor of photophosphorylation in spinach chloroplasts.
abstract: 5-O-β-D-galactopyranosyl-7-methoxy-3',4'-dihydroxy-4-phenylcoumarin isolated from Exostema caribaeum (Rubiaceae) has been found to act as an energy-transfer inhibitor in spinach chloroplasts. ATP synthesis and phosphorylating (coupled) electron flow were inhibited by 89 and 72%, respectively, at a concentration of 400 μM. H(+)-uptake, basal and uncoupled electron transport were not affected by the coumarin. The light-activated Mg(+2)-ATPase activity from bound membrane thylakoid chloroplasts was slightly inhibited by the coumarin. Also, the heat-activated Ca(+2)-ATPase activity of the isolated coupling factor protein was insensitive to this compound. In chloroplasts partially stripped of coupling factor 1 by an EDTA treatment, the coumarin showed a restoration of the proton uptake process. These results suggest that the 4-phenylcoumarin under investigation inhibited phosphorylation in chloroplasts by specifically blocking the transport of protons through a membrane-bound component or a carrier channel (CFO) located in a hydrophobic region at or near the functional binding site for the coupling factor 1.
authors.affiliation: Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, D.F.04510, México, México.
authors.forename: M R
authors.initials: MR
authors.lastname: Calera
authors.forename: R
authors.initials: R
authors.lastname: Mata
authors.forename: A L
authors.initials: AL
authors.lastname: Anaya
authors.forename: B
authors.initials: B
authors.lastname: Lotina-Hennsen