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M Fabian

Publications and source records attributed to M Fabian.

46 records · Page 3Linked to original sources
PubMed1966

Specialized receptive fields of the cat's retina.

Three new types of receptive field have been found in the cat's retina. The responses of these fields to flashing lights and moving objects suggest that the manner in which they code visual information may be quite different from that of the center-surround fields described in previous studies. These "specialized" fields were all found in the area centralis. A definite functional difference, corresponding to the known anatomical difference, between this region and the rest of the retina, is suggested.

Animals↗
PubMedDate not supplied

[Temperature dependence of protein globule polarization and electron transport in preparations of photosynthetic reaction centers from Rhodopseudomonas sphaeroides].

Differential "light-minus-dark" spectra were obtained for reaction center (RC) preparations cooled in the light and in the dark at 77 K. The two types of preparations were found to display different spectral features in the spectral regions 760-770, 790-810, 880-990 nm. Differences in the spectra of the two types were found to exist in preparations cooled to temperatures below 120-100 K, whereas at temperatures above 130 K such differences were not observed. The observed spectral changes may be associated with the polarization processes occurring in the RC globule. Samples cooled in the light and in the dark show different temperature dependencies of the efficiency of electron transfer to the secondary quinone acceptor. The differences are irreversible after cooling to temperatures below 170 K, and reversible after cooling to 180-200 K. It is postulated that the observed kinetic changes are reflections of changes in the configuration of the acceptor complex of the RC. The possible existence of a correlation between the polarization processes in the protein globule and the structural configurations of the RC is discussed.

Bacterial Proteins↗
PubMedDate not supplied

[Protein fluorescence of photosynthetic reaction centers from Rhodopseudomonas sphaeroides].

Luminescence emitted by tryptophan residues of reaction center (RC) preparations was studied. The RG preparations were isolated from the photosynthetic bacterium Rhodopseudomonas sphaeroides by treatment with lauryl dimethyl amine oxide (LDAO). After excitation at lambda 280 nm the quantum yield of luminescence is 0,02. It is shown that 60% of tryptophanyls are located inside the protein globule in the surrounding of relaxating polar groups and the rest approximately 40% on the outer surface of the globule--predominantly in the positively charged region of the LDAO-RC protein--in the surrounding of protein-bound water molecules. There is a correlation between the pH dependencies of the position of the peak of luminescence from tryptophanyls and effectivity of electron transfer from the primary (quinone) to secondary acceptor. The two parameters are invariant at pH from 7 to 9 and vary at pH less than 7 and pH greater than 9. The phenomena responsible for the observed correlation are discussed on the basis of pH-dependent changes in the RC protein which govern electron transport activity at the reaction center.

Bacterial Chromatophores↗
PubMedDate not supplied

[Effect of pH on photoinduced electron transport in reaction center preparations from Rhodopseudomonas sphaeroides].

The effect of ph on kinetics of photo-induced electron transport process was studied on reaction centre preparations extracted by LDAO treatment of R. sphaeroides chromatophores (strain 1760-1). Reaction centre activity was found to be optimal at pH 7--9. Within this range of pH, the rate constant, KX1X2, for electron transfer from the primary FeQ acceptor complex (X1) to the secondary quinone acceptor X2 appeared to be invariant. On pH lowering from 7 to 5 the value of KX1X2 increases by several times. It abruptly drops, when pH is increased from 9 to 9.5. The nature of these phenomena including influence of pH on KX1X2 value is discussed.

Binding Sites↗
PubMedDate not supplied

[Light-induced changes in pH and buffer capacity in reaction center preparations of Rhodopseudomonas spheroides].

In experiments with reaction centers (RC) preparations of Rps. sphaeroides, strain 1760-1, pH of the suspension medium was found to change under continuous light excitation. The concentration of hydrogen ions starts to decrease fastly (t1/2 = 2--4 s) after the light is on, whereupon it increases slowly, to a steady-state level, within t1/2 = 5--7 min. During the fast phase 0.3 microM H+/1 microM of RC are absorbed and 7--8 microM H+/1 microM of RC are released under the slow phase. The fast phase is suppressed by ortho-phenantroline (10 mM)--an inhibitor of electron transfer from the primary (Fe-quinone complex) to the secondary (quinone) electron acceptors. Glutaraldehyde which is known to modify a protein structure of the RC inhibits the slow phase. The obtained data suggest that fast light-induced pH changes are due to a H+ uptake by the secondary quinoid anion-radical products; slow pH changes are ascribed to structural changes within the RC complex, which lead to a pK shift and/or changes in the amount of dissociating groups on the protein interfacial surface. The conclusion was supported by an observation of light-induced changes in buffer capacity of an RC suspension and by a light-induced increase in the amount of SH-groups titrated by 5.5-dithio-bis(2 nitro)-benzoic acid. The role of conformational dynamics of photoactive pigment--protein complexes in the functions of the RC is discussed.

Bacterial Proteins↗