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F F Litvin

Publications and source records attributed to F F Litvin.

66 records · Page 4Linked to original sources
PubMedDate not supplied

[Analysis of photosynthesis light curves under continuous illumination].

A mathematical description of the photosynthesis light curve is proposed taking into account the type of photosynthetic unit (PSU) organization (unicentral or multicentral), energy migration between the PSU, and the nonlinear character of the dark process limiting the rate. In the case of unicentral PSU the light curve is described by the expression: I = v (1--yv)/(1--v) where I is light intensity; v is relative rate of photosynthesis (relative to the maximal rate); y is the parameter which determines the shape of the curve. Its value depends on the efficiency of energy migration between PSU and on the ratio of the limiting dark reactions rates. The variations of the value from 1 to 0 give different known types of light curves. Coordinates are proposed in which the curves for multicentral and unicentral PSU are distinguished and parameter is estimated. Experimental light curves for a number of marine algae correspond to the supposition of the PSU unicentral organization, with y = 0.9.

Darkness↗
PubMedDate not supplied

[Photosynthesis light curves under flash illumination].

Light curve of the multicentral model of photosynthetic unit (PSU) has been obtained. The shape of the curve depends on the efficiency of energy migration between PSU--for the unicentral PSU, and on the number of traps for multicentral PSU. The criteria distinguishing between the two models are proposed. If the efficiency of energy migration between PSU is no more than 0,7, then, there exist ony unicentral and bicentral PSU.

Kinetics↗
PubMedDate not supplied

[Inhibitory effect of blue and ultraviolet light on photoinduced changes in the pH of a suspension of Halobacterium halobium cells].

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.

Bacteriorhodopsins↗
PubMedDate not supplied

[Photochemical transformations of bacteriorhodopsin].

Results of experimental studies of bacteriorhodopsin photochemical transformations of purple membranes at low temperatures are presented. A scheme of reactions of light-adapted bacteriorhodopsin is proposed, some regularities of its phototransformations are considered. Relationships between quantum yields of direct and reverse photoreactions and absorption spectra of the states initiated during phototransformations of the pigment are determined. Proceeding from spectroscopic data the mechanisms of photochemical processes in bacteriorhodopsin are discussed. The author's and literature data point to the participation of retinal structural changes, of alterations in retinal interactions with opsin and of proton in bacteriorhodopsin photoreactions.

Bacteriorhodopsins↗
PubMedDate not supplied

[Energy migration in a pigmented protochlorophyllide complex].

Data are analysed concerning energy migration between protochlorophyllide and chlorophyllide formed in etiolated leaves. It is found that phototransformation of the precursor proceeds in the pigment complexes similar to the multicentric photosynthetic unit. The complexes comprise no more than 26 molecules of the active form of protochlorophyllide P650 and two molecules of minor forms of P628 and P639 on the average with mean intermolecular distances 3 nm.

Chlorophyll↗
PubMedDate not supplied

[FLuorescence of photoactive bacteriorhodopsin].

Fluorescence characteristics of all-trans-bacteriorhodopsin (BR570), 13-cis-BR (BR560), and the intermediate of the BR cycle (P585) are obtained by measuring variable fluorescence in the course of their phototransformations. The fluorescence spectra (lambda greater than 580 nm) have a maximum at 720, 730 and 740 nm, their respective excitation spectra with a maximum of 578, 565 and 585 nm coincide with the absorption spectra of the three states. The emission quantum yield for P585 is approximately 10(-4) at -62 degrees C and 4 +/- 2 10(-4) for BR560 at -196 degrees C. The effect of sharp increase of BR570 fluorescence quantum yield (from less than or equal to 10(-4) to approximately 10(-3)) under action of light at -196 degrees C (photoactivation or induction of emission) is found which points to the existence of photoprocess parallel to the photoconversion of BR570 into P600 (formula: see text). The emission of BR560 is not photoactivated. The photoactivated state BR570 is not identical with pseudo-BR of Gillbro et al., (1977) which has a maximum in the excitation spectrum at 597 nm. The greater part of the red fluorescence of the membrane belongs to the minor nonphotoactive forms of BR (B578, B630) with relatively high fluorescence yield (greater than or equal to 10(-2) at -196 degrees C). The fluorescence characteristics of BR are discussed in the framework of a scheme in which the existence of an intermediate excited level common for the emission and photoconversion and a ground level common for the initial state and photoproduct is suggested.

Bacteriorhodopsins↗
PubMedDate not supplied

[Fine structure of the fluorescence spectra of chlorophyll a, protochlorophyll, and their pheophytins following selective laser irradiation].

Fine structure fluorescence spectra of solutions in diethyl ether of chlorophyll a, pheophytin a, protochlorophyll and protopheophytin were obtained and studied at 4.2 K under stimulation with reconstructed laser on dyes. Dependence of the spectrum on lambda excit was studied and oscillation frequencies in basic and excited electron states were determined. Frequency dependence on the character of molecular surrounding was exemplified by chlorophyll a.

Chlorophyll↗
PubMedDate not supplied

[New intermediate reactions in the process of protochlorophyllide photoreduction].

It has been found that formation of non-fluorescine intermediate product with the absorption maximum 690 nm during photochemical hydration of protochlorophyllide in ethiolated plant leaves can also proceed at -196 degrees C. During dark transformation of this product two forms of the pigment with the fluorescence maxima 695 and 685 nm are initiated, the first one preceding. The dependence of the spectral changes discovered on the light spectral composition is interpreted as a consequence of switching on of the parallel reactions of precursors or as a result of photoreversible reaction into chlorophill biosynthesis.

Chlorophyll↗
PubMedDate not supplied

[Component breakdown of the absorption and fluorescence spectra of green bacteria].

The total number, band widths, absorption and fluorescense peak positions of bacteriochlorophyll forms in green bacteria were identifyed using computer curve analysis, Stepanov's relation and low temperature derivative spectroscopy. The identified pigment forms are the following (the lower index--absorption peak position, the upper--fluorescence peak position) (see article). The energy of the O-O transitions in the row of native forms of bacteriochlorophyll enumerated above changes for a constant equal to 80 cm-1. It is believed that the bacteriochlorophyll aggregate in the reaction center complex of green bacteria consists of 7 molecules.

Bacteriochlorophylls↗
PubMedDate not supplied

[Induction of fluorescence of a single chloroplast in an entire cell of the green alga Haematococcus pluvialis].

The fluorescense induction time-course of a single chloroplast in an intact cell of the green alga Haematococcus pluvialis has a line structure, which could not be observed in a suspension because of the superposition of the emissions of many cells. The time-course of the induction includes 12 well separated parts in the time range from several milliseconds to several minutes. Parameters of the fine structure depends on the physiological state of the cell, intensity and wave-length of the exciting light.

Chlorophyta↗