[Light-induced changes in quantum yields of the photochemical cycle of conversion of bacteriorhodopsin and transmembrane proton transfer in cells of Halobacterium halobium]. / Fotoindutsirovannye izmeneniia kvantovykh vykhodov fotokhimicheskogo tsikla prevrashchenii bakteriorodopsina i transmembrannogo perenosa protonov v kletkakh Halobacterium halobium.

It was found that the rate of proton efflux from the cells, vH+, and the turnover number of bacteriorhodopsin photoconversion cycle per second, vM, are gradually decreased during continuous illumination of Halobacterium halobium with orange light (550-650 nm, 10(3) W/m2). The steady-state value of vH+ after 3 min of illumination is 3 times lower than vH+ at the 1st second of illumination. At the same time the concentration of the photochemical cycle intermediate, M412, the quantum yield of its formation, phi M, and the quantum efficiency of proton efflux, phi H+, are decreased (phi M and phi H+ up to 3-4-fold), whereas the concentration of the initial form of bacteriorhodopsin, BR570, and lifetime of M412, tau, are increased. These light-induced effects are abolished by uncoupler, carbonylcyanide m-chlorophenylhydrazone (CCCP) and are enhanced by the phosphorylation inhibitor, N,N'-dicyclohexylcarbodiimide (DCCD). This suggests that the observed changes of M412 and BR570 concentrations, tau, VH+, VM, phi M and phi H+ are due to the light-induced changes in the transmembrane electric potential, delta psi, and in pH inside and outside the cell, which control the photochemical cycle reactions. The decrease of phi M and phi H+ is discussed on the basis of an earlier proposed scheme of the branched photochemical cycle. It is assumed that the back reactions of the cycle (shunts) not coupled with the transmembrane proton translocation, e.g. conversion of L550 (P550) into BR570 without M412 formation, etc., become more probably at high values of the proton electrochemical potential gradient.

[Inhibitory effect of blue and ultraviolet light on photoinduced changes in the pH of a suspension of Halobacterium halobium cells]. / Ingibiruiushchee deistvie sinego i ul'trafioletovogo sveta na fotoindutsirovannye izmeneniia pH suspenzii kletok Halobacterium halobium.

It was found that when switching on blue and UV light with the green one at the background decreased the acidification of Halobacterium suspension sensitized with bacterirhodopsin. Three facts are responsible for the acidification decrease. 1. At high intensity of the background green light (above 10(2)/Wt/m2) the effect predominates, which is conditioned by the action of blue light on the intermediate of the photochemical cycle of bacteriorhodopsin P419 (M412). Phototransformation of the latter prevents the transmembrane transfer of H+. 2. At high intensities of shortwave light (10(3)Wt/m2) alkalization of the suspension sensitized with unidentified pigment is observed. 3. At low intensities of blue and UV light (10 Wt/m2) the effect with the maximum in the action spectrum at 390 nm predominates. It is increased after preillumination of Halobacteria with green light and after short-term incubation (to 1-2 hours at 20 degrees C) of the cells with dicyclohexylcarbodiimide. It is inhibited with dinitrophenol. The effect is suggested to result from the photo-induced increase of cell membrane permeability for H+. Judging by the action spectrum it may be involved in the phototaxis of Halobacteria.