1Departamento de Química Universidade Federal de São Carlos (UFSCar), 13565-905, São Carlos-S. P., Brasil.
2Facultad de Química, Departamento de Bioquímica,, Universidad Nacional Autónoma de México, México, D.F. C.P. 04510, México.
* Correspondence author, Facultad de Química, 1Departamento de Bioquímica, Universidad Nacional Autónoma de México (UNAM), Ciudad Universitaria, C.P. 04510, México D. F., México. E. Mail: blas@servidor.unam.mx
Flindersine (1) and N-methyl-flindersine (2) were isolated from Hortia superba. Both compounds inhibited the synthesis of ATP and non-cyclic electron transport, i.e. they behaved as Hill reaction inhibitors. Both alkaloids inhibited electron flow through PSII. The effect of the alkaloids on the partial PSII reactions was measured as under: from water to oxidized DCPIP, water to sodium silicomolybdate and from reduced DPC to oxidized DCPIP. The results demonstrated that their inhibition site was at QB., since the ectron flow from water to Pheophytin was not affected. Furthermore, alkaloid 2 had another site of inhibition located at PQH2 oxidation site, the b6f complex. The polarographic results were corroborated by Chl a fluorescence measurements; in thylakoids, the alkaloids changed the shape of the Kautsky curve. The OJIP test indicated that the behavior of alkaloids 1 and 2 was similar to DCMU. In addition, alkaloid 2 was less active than 1. The main inhibition site of 2 was located at the PQH2 site of oxidation within the b6f complex.
Alkaloids, chlorophyll a, findersine, fluorescence, Hortia superba, N-methyl-flindersine, PS II and b6f inhibitors
