Dynamics of excitation in the photosystem I of cyanobacteria: transfer in the antenna, capture by the reaction site, and dissipation

The structure of a complex of photosystem I (PSI) of cyanobacteria and the mechanisms of the functioning of the antenna and PSI reaction site were described. The complex of PSI in thylakoids of cyanobacteia is organized as a trimer whose antenna is enriched in long-wave chlorophylls. The energy absorbed by these chlorophyls migrates to P700, inducing its oxidation. Long-wave chlorophyls are also involved in the dissipation of excessive energy; both the cation radical of P700 and the triplet of P700 effectively quench the fluorescence of long-wave chlorophyll of PSI. The energy exchange between the antennas of monomers in the trimer of PSI stimulates the dissipation of electron excitation energy, protecting the complex against photodestruction. The kinetics of energy migration in the antenna and charge separation in the reaction site of PSI trimers was studied using subpicosecond spectroscopy. Long-wave chlorophylls of PSI do not substantially affect the energy migration in the heterogeneous antenna of PSI but slow down the capture of energy of P700. The separation of changes in the reaction site of PSI is the most rapid among the known reaction sites.     

Extinction of the defensive conditioned reflex in cats after lesioning the endopeduncularis nucleus]

Influence of bilateral destruction of nucleus entopeduncularis on the extinction of conditioned avoidance was studied in 10 adult cats. It was shown that bilateral destruction of the nucleus entopeduncularis led to a disturbance of storage of the previous conditioning and facilitated repeated extinction.     

Novel aryl and heteroaryl substituted N-[3-(4-phenylpiperazin-1-yl)propyl]-1,2,4-oxadiazole-5-carboxamides as selective GSK-3 inhibitors

Synthesis, biological evaluation, and SAR dependencies for a series of novel aryl and heteroaryl substituted N-[3-(4-phenylpiperazin-1-yl)propyl]-1,2,4-oxadiazole-5-carboxamide inhibitors of GSK-3beta kinase are described. The inhibitory activity of the synthesized compounds is highly dependent on the character of substituents in the phenyl ring and the nature of terminal heterocyclic fragment of the core molecular scaffold. The most potent compounds from this series contain 3,4-di-methyl or 2-methoxy substituents within the phenyl ring and 3-pyridine fragment connected to the 1,2,4-oxadiazole heterocycle. These compounds selectively inhibit GSK-3beta kinase with IC(50) value of 0.35 and 0.41 microM, respectively.     

Complex of brain D-phosphoglycerate mutase and gamma enolase and its reactivation by D-glycerate 2,3-bisphosphate

The dissociabilities of dimeric gamma enolase, alpha enolase, and phosphoglycerate mutase of brain origin were tested using fluorescein isothiocyanate attached covalently to these enzymes. The dissociation constant of dimeric gamma enolase is lower (Kd = 0.03 microM) than that of the alpha enolase (Kd = 3 microM), while dimeric mutase seems to be nondissociable in the concentration range 0.1-10 microM, at pH 7.3 in 50 mM imidazole buffer at 20 degrees C. Interaction of neuron-specific gamma enolase with D-phosphoglycerate mutase was detected with the same fluorescence-labeling technique as well as by a kinetic analysis. The determined dissociation constant of the enolase-mutase complex was found to be in the range 5-40 microM, independent of the technique used. A mixed type of inhibition in the binding of D-glycerate-2-P and mutase to the D-glycerate-2-P binding site on enolase was observed in the absence of D-glycerate-2,3-P2. However, the inhibition of the enolase activity by brain D-phosphoglycerate mutase in the D-glycerate-2-P----phosphoenolpyruvate transformation is almost fully reverted by D-glycerate-2,3-P2, probably via the proper coordination of the active centers in the ternary complex of enolase, D-phosphoglycerate mutase, and their common intermediate, D-glycerate-2-P. The mechanism of intermediate transfer by consecutive enzyme pairs in a nondivergent metabolite flux (around the transformation of D-glycerate-2-P) is examined and conclusions of the present experiments are compared with the results of an extended analysis performed earlier with a divergent metabolite flux (around the transformation of multiusage triosephosphates, D-glyceraldehyde-3-P, and dihydroxyacetone phosphate).     

Theory of helix-coil transition on DNA-ligand complexes: the effect to two types of interaction of ligand on the parameters of transition

The effect of ligand interacting with native DNA by two types on the parameters of helix-coil transition in homopolymers is considered using the most probable distribution method (Yu.S. Lazurkin et al., Biopolymers 1970). It is shown that at a small relative concentration of ligand the melting enthalpy (delta H) of DNA may be obtained from the universal formula which contains only values directly known from the experiments. It is shown that the formula for the change of melting temperature and width of melting range depending on the total ligand concentration in solution is converted into the corresponding formulae which are defined for the case when only one type of interaction of ligand and DNA is considered.     

Isolation and characterization of a cellobiose dehydrogenase formed by a asporogenic mycelial fungus INBI 2-26(-)

A nonsporulating fungus isolated from dioxine-containing tropical soils forms cellobiose dehydrogenase, when grown in media supplemented by a source of cellulose. The enzyme purified to homogeneity by SDS-PAGE (yield, 43%) had an M(r) of 95 kDa; its pH optimum was in the range 5.5-7.0; more than 50% activity was retained at pH 4.0-8.0 (citrate-phosphate buffer). The absorption spectrum of the enzyme in the visible range had the characteristic appearance of flavocytochrome proteins. Cellobiose dehydrogenase oxidized cellobiose and lactose (the respective K(M) values at pH 6.0 equaled 4.5 +/- 1.5 and 56 microM) in the presence of dichlorophenolindophenol (K(M) app = 15 +/- 3 microM at pH 6.0) taken as an electron acceptor. Other sugars were barely if at all oxidized by the enzyme. Neither ethyl-beta-D-cellobioside, heptobiose, nor chitotriose inhibited the enzymatic oxidation of lactose, even under the conditions of 100-fold molar excess. The enzyme was weakly inhibited by sodium azide dichlorophenolindophenol reduction and exhibited affinity to amorphous cellulose. At 55 degrees C and pH 6.0 (optimum stability), time to half-maximum inactivation equaled 99 min. The enzyme reduced by cellobiose was more stable than the nonreduced form. Conversely, the presence of an oxidizer (dichlorophenolindophenol) decreased the stability eight times at pH 6.0. In addition, the enzyme acted as a potent reducer of the single-electron acceptor cytochrome c3+ (K(M) app = 15 microM at pH 6.0).     

Degradation of lignin-carbohydrate substrate by soil fungi--producers of laccase and cellobiose dehydrogenase

The growth of nonsporulating mycelial fungi INBI 2-26(+), producer of laccase; INBI 2-26(-), producer of cellobiose dehydrogenase; and their mixed culture on lignin-carbohydrate substrates under conditions of submerged fermentation were studied. The degrees of degradation of lignin, cellulose, and hemicellulose of cut straw over 23 days amounted to 29.8, 51.4, and 72% for the laccase producer; 15.8, 33.9, and 59.1% for the cellobiose dehydrogenase producer; and 15.8, 39.4, and 64.5% for the mixed culture, respectively. The laccase activity in the medium when strain 2-26(+) was cultivated individually reached its maximum on day 28; the activity of cellobiose dehydrogenase of strain 2-26(-), on days 14 to 28. A method for determining cellobiose dehydrogenase activity in the presence of laccase was developed. In the mixed culture, both enzymes were formed; however, the level of laccase synthesis was 1.5-fold lower compared to that of strain 2-26(+), while synthesis of cellobiose dehydrogenase was similar to that of the corresponding producer. Cellobiose dehydrogenase failed to boost the action of laccase while degrading the lignin of straw.     

New Functions of a Well-Known Protein: Prothymosin α Is Involved in Protecting Cells from Apoptosis and Oxidative Stress

Recent studies have revealed two new functions of prothymosin α (ProTα), a well-known protein and a subject of intense research. In addition to acting as an immunomodulator and stimulating cell proliferation, ProTα is involved in protecting the cell from apoptosis and regulating the expression of oxidative stress defense genes. The review considers the methods and approaches used to demonstrate the two new functions of ProTα.