[What does the "screening hypochromism of chromophores" actually imply]. / Chto zhe samom dele oznachaet "ékranirovochnyi gipokhromizm khoromoforov"?

The groundlessness of the conception of "screening hypochromism" from the viewpoint of physics is shown.

[What does the "screening hypochromism of chromophores" actually imply?]. / Chto zhe samom dele oznachaet "ékranirovochnyi gipokhromizm khoromoforov"?

Comments to the article of N.L. Vekshin "Screening hypochromism of chromophores in macromolecular biostructures (Biophysics, 1999. V. 44. P. 45.) are given. The incorrectness of the main propositions and results of the study is shown.

[Effect of chain length on formation of a double-layer structure of Z-(Gly-Pro-Gly)n-OMe oligotripeptides]. / Obrazovanie struktury dvoinogo sloia v riadu oligotripeptidov Z-(Gly-Pro-Gly)n-OMe pri posledovatel'nom udlinenii molekuliarnoi tsepi.

Effect of chain length on the formation of the double-layered sheet in synthetic oligotripeptides Z-(Gly-Pro-Gly)n-OMe (n = 1,2,3,4) in the solid state has been studied by the IR-spectroscopy method. The major spectral features characteristic for the polymer structure was found in the oligomer spectra beginning with that of hexapeptide (n = 2). So a minimum peptide length when peptide chains are still able to adopt the double-layered sheet conformation in the solid state includes two triplets. The result is similar to that we have revealed early by investigation of the collagen-like triple helix formation in the oligomer series Z-(Gly-Pro-Pro)n-OMe. The double-layered sheet structure of the hexapeptide was found completely regular as that of the polymer. So the formation of the double-layered sheet structure unlike the formation of the triple-helical structure occurs at once without gradual ordering of interpeptide bonds and molecular packing by further increasing of the triplet number in oligomer chains. Additional information concerning specific incorporation of bound water in the double-layered sheet and water influence on peptide packing has been derived from analyses of hydration effect on the oligotripeptide IR-spectra especially on the components of the amide I band.

[Thermodynamic studies of triple-helical structures of the collagen type in oligotripeptides during study of molecular chain elongation]. / Termodinamicheskie issledovaniia trekhspiral'noi struktury kollagenovogo tipa v oligotripeptidakh pri posledovatel'nom udlinenii molekuliarnoi tsepi.

The conformational transition collagen-like triple helix in equilibrium with chains of oligotripeptides Z-(Gly-Pro-Pro)n-OMe with n = 6, 7, 8 in water by variation of solution temperature and sample concentration has been studied using IR-, CD-spectroscopy and microcalorimetry methods. The straight line correlation between the obtained value of the transition enthalpy and entropy and the number of the triplets (3n - 2), involved in the interpeptide set of hydrogen bonds was revealed. Evidently the effect of terminal groups is really weak in this case, and the interpeptide bonds of the triple helix may be regarded as equivalent one another. The estimated cooperative block of nucleation corresponds in length to the one full turn of the superhelix. The state diagrams of the oligotripeptides with n = 6, 7, 8 in aqueous solution are presented.

[Effect of the length of molecular chain on the formation of triple-helical collagen-like complex in solutions. The role of water in the formation of triple helix]. / Vliianie dliny molekuliarnoi tsepi na obrazovanie trekhspiral'nogo kompleksa kollagenovogo tipa v rastvorakh. Rol' vody v formirovanii troinoi spirali.

Effect of molecular chain length on the formation of the collagen-like triple helix in synthetic oligotripeptides Z-(Gly-Pro-Pro)n-OMe (n-1,2,3,...,8) in solutions has been studied, using IR- and CD-spectroscopy methods. The helix formation under different conditions is investigated: in the presence of a relatively inert solvent (chloroform), in the presence of a hydrogen bond acceptor (dioxan), in the presence of a hydrogen bond acceptor and donor as well (ethanol). Special attention is paid to the role of water in the formation of a stable triple-helical structure. Successive stages in the formation of a stable triple-helical structure in solutions during elongation of the peptide chain is revealed, which may be correlated with the helix nucleation process. A minimum peptide length, when peptide chains are still able to associate in the collagen-like triple-helical complex, involves three triplets for oligomers in chloroform solution, four triplets for oligomers in dioxan and ethanol solutions, six triplets for oligomers in aqueous solution. The main features of the completed triple-helical structure in water are found already in the oligotripeptide with n-8, where the formation one full turn of the superhelix is finished.

[Formation of a hydrate structure in the collagen-like triple helix upon hydration]. / Formirovanie gidratnoi struktury troinoi spirali kollagenovogo tipa pri gidratsii.

By the IR-spectroscopy method successive stages of hydrate envelope formation of the collagen-like triple-helical structure of the monodisperse synthetic polytripeptide Z-(Gly-Pro-Pro)8-OMe were studied. The multistep-type process is followed by isomorphic transitions of the triple-helical structure and by the increasing of hydrogen bond strength.

[Investigation of the effects of dehydration on bacterial rhodopsin by laser resonance Raman spectroscopy]. / Issledovanie vliianiia degidratatsii na bakterial'nyi rodopsin metodom rezonansnoi spektroskopii kombinatsionnogo rasseianiia sveta.

Using laser resonance Raman spectroscopy the influence of water on the structure of the chromophore centre in bacteriorhodopsin from Halobacterium halobium has been studied. The absorption band has been found to shift from 568 nm to 506 nm due to local protein changes in the chromophore centre near Schiff base bounding retinal with the lysine residue. These changes are not accompanied by the Schiff base deprotonation. Dehydration decreases essentially the reaction rate of the cis in equilibrium trans isomerization processes. In the dry state the potential barriers of the cis in equilibrium trans transition reaction turns out to be higher than that of the reverse reaction. As a result the equilibrium shifts to the cis-retinal form. Comparison of the Raman spectra of the M412 intermediate in wet and dry states of purple membranes leads to the conclusion that in water suspensions of purple membranes the chromophore state of the M412 intermediate is closer to cis- than to trans-retinal.

[Structural differences in the collagens of Rana frog species with dissimilar temperature ecology. The contribution of carbohydrate components to collagen molecular thermostability]. / Strukturnye razlichiia kollagenov u nekotorykh vidov liagushek roda Rana s neodinakovoi temperaturnoii ékologiei. Vklad uglevodnykh komponentov v termostabil'nost' molekul kollagena.

Skin procollagens in two species groups of frogs of the genus Rana - brown frogs (4 species) and green frogs (3 species) distributed in European and Asiatic parts of the USSR have been compared. A geographic intraspecific variation in collagen characteristics (two geographic populations of the pond frog Rana nigromaculata) is revealed. Intergroup differences in the thermal denaturation of collagens established by means of methods of circular dichroism and microcalorimetry are significant. Such differences within both the groups are not so visible. With the species studied, carbohydrate components contents in procollagen vary. Interspecific differences in the procollagen thermostability correlate with the thermal ecology of frogs and seem to be associated with the availability of carbohydrates.

[Aggregation of poly-L-proline in aqueous solution]. / Agregatsiia poli-L-prolina v vodnom rastvore.

Infrared spectra were measured for both aqueous (D2O) solution and the solid state of form II poly-L-proline in the amide I region as a function of the temperature. The temperature range includes the region where a precipitation is known to occur. From the analysis of spectra of hydrated films and aqueous solutions at different temperatures one can see that there are some peptide C = O-groups which are bounded with water. From this study it has been concluded that poly-L-proline exists in aggregate form even at temperatures lower that required for precipitation. It is supposed that poly-L-proline forms the aggregates including at least 40--50 polypeptide chains with hexagonal packing. At heating crystallisation of such aggregates occurred and it causes precipitation of poly-L-proline II.

[Modification of the retina photoreceptor membranes and temperature stability of rhodopsin]. / Modifikatsiia fotoretseptornykh membran setchatki i temperaturnaia stabil'nost' rodopsina.

The effect of modification of photoreceptor membranes of the bovine retina on the termodynamical parameters that characterize heat denaturation of rodopsin was studied. The highest increase of the rate constant and the corresponding maximal drop of the free energy change of heat denaturation of the pigment were obtained by using 7 M urea or 25% Triton X-100 in the presence of 5.10(-4) M EDTA. After chipping off one third of the protein from the rodopsin molecule by papain treatment a significant decrease of the slope of the Arrenius curve and a maximal decrease of entropy change compared to the parameters known for heat denaturation of the pigment in native photoreceptor membranes were found. Modification of the lipid components of the photoreceptor membranes (treatment with Triton X-100 and phospholipase C) reduced the thermostability of rodopsin. Maximal changes were obtained at Triton X-100 concentrations 0.1--1%, further concentration increas (1--25%) did not lead to significant changes. Phospholipase C treatment resulted in a decrease of free energy change and an increase of entropy change without affecting entalpy changes, accompaning the heat denaturation of rodopsin. Bivalent cations (Ca2+, Mg2+) increased the termostability of rodopsin both in photoreceptor membranes and in solutions to 25% Triton X-100.

[Picosecond flash photolysis of Halobacterium halobium bacteriorhodopsin at room and low temperatures]. / Pikosekundnyi flesh-fotoliz bakteriorodopsina iz Halobacterium halobium pri komnatnoi i nizkikh temperaturakh.

The primary stage of photoexcitation of bacteriorhodopsin from Halobacterium halobium upon the action of ultrashort (tau equal to 25 ps) laser impulse of 530 nm wavelength and of energy 2.5.10(-3) J has been studied. The primary photoproduct with a maximum of 630 nm is shown to occur in the differential spectrum in a time less than 25 ps both at room temperature (+20 degrees C) and at a low temperature (-150 degrees C).

[IR-spectroscopic study of cytochrome C-phospholipid lipoprotein and proteolipid model membranes]. / Isseldovanie tsitokhrom-c-fosfolipidnykh lipoproteinovykh i proteolipidykh model'nykh membran metodom IK-spektroskopii

It is shown by the methods of IR-spectroscopy and peptide hydrogen-deuterium exchange that a) considerable changes in the protein spectra occur (beta-conformation in the protein structure appears) during the interaction in water of cytochrome c molecules with lipid membranes containing negatively charged polar groups; b) further significant changes of the protein spectrum occur under the action of 1% OsO4 and heating up to n plus 95 degrees C; c) the conformational state of the pure protein in water; after the treatments of the proteolipid memebranes with 1% OsO4 and heating up to n degrees C no significant changes of protein spectrum occur, that may suggest hydrophobic interactions between the protein and lipids; d) the treatment of both pure cytichrome c and the model membranes with 1% glutaraldehyde, 30, 60% ethanol and acetone solutions in water does not reveal substantial changes in IR-spectra of the protein moiety.