[Proton absorption by chloroplasts in cyclic electron transport catalyzed by photosystem I in anaerobic conditions].

Proton absorption by pea chloroplasts in anaerobic conditions under inhibition of non-cyclic electron transport with diurone is investigated. 2,6-dichlorophenolindophenol (DCPIP) and tetramethyl-p-phenylenediamine (TMPD) are used as cofactors of cyclic electron transport. Proton absorption in the absence of methylviologen is found to take place only in experiments with DCPIP, while in the presence of methylviologen it is observed with both cofactors, being considerably higher is the case of TMDP. In experiments with DCPIP absorbed protons comprise two fractions differing in the rate of the output of particles from tilakoids and in the number of the particles. The presence of these two fractions is suggested to be due to the well-known fact of the presence of two sites of electrone intake into electron transport chain by reduced DCPIP. On the basis of dependency of fraction composition on DCPIP concentration and of the mode of dibromothimoquinone, gramicidin D and antimycin A action on these fractions, it is suggested that protons of "a slow" fraction are capable to participate preferably in the ATP synthesis.