Conformational analysis of galanin using end to end distance distribution observed by Förster resonance energy transfer

The structural dynamics of the flexible neuropeptide galanin in solution were studied by Förster resonance energy transfer measurements at different temperatures by time-resolved fluorescence spectroscopy to determine its conformational heterogeneity. Endogenous tryptophan at position 2 acted as the fluorescent donor and the non fluorescent acceptor dinitrophenyl or the fluorescent acceptor dansyl were selectively attached to lysine 25 in porcine galanin. The coexistence of different structures of the neuropeptide galanin in trifluoroethanol solution was revealed by the model independent analysis of the distribution of relaxation times from the time-resolved resonance energy transfer data. Multiple conformational states are reflected by distinct end-to-end distance populations. The conformations differ in mean donor-acceptor distance by about 15 Å, and are consistent with the extended and folded backbone conformations of two α-helical regions separated by a flexible hinge. The effect that the labelling of galanin has on binding to the receptor was also evaluated. DNP-galanin showed the same high affinity to galanin receptors as unlabelled galanin, whereas DNS-galanin had significantly reduced affinity.     

Mechanism of the radioprotective effect of catecholamine receptor agonists. Inclusion in the radioprotective effect of both subtypes of alpha-adrenoreceptors

alpha-Adrenoceptor agonists of both main groups, i. e. arylalkylamines and imidazolines, have a pronounced radioprotective effect. Their chemical analogs, which fail to stimulate alpha-adrenoceptors, do not protect mice. The effect of phenylephrine, adrenaline, and noradrenaline comes into play via alpha 1-adrenoceptors and that of clonidine, via alpha 2-adrenoceptors and also via alpha 1-adrenoceptors. Adrenoceptor agonists can probably manifest their radioprotective action via both subtypes of alpha-adrenoceptors. Possible intracellular mechanisms of the radioprotective action are discussed.     

Spectroscopic investigations of the single tryptophan residue and of riboflavin and 7-oxolumazine bound to lumazine apoprotein from Photobacterium leiognathi

Spectroscopic techniques have been applied to investigate the conformation, local structure, and dynamic properties of the apoprotein of the lumazine protein from Photobacterium leiognathi and the holoprotein reconstituted with either the natural ligand 6,7-dimethyl-8-ribityllumazine or the closely related analogues riboflavin and 6-methyl-7-oxo-8-ribityllumazine (7-oxolumazine). The analogues are bound similarly to the natural prosthetic group. They exhibit similar shifts on binding in their absorption and fluorescence spectra, single-exponential fluorescence decays, and no independent motion from the protein as evident from a long-lived anisotropy decay (single-exponential phi = 10 ns, 20 degrees C) and high initial anisotropy. Steady-state anisotropy measurements result in similar KD's (40 nM, 20 degrees C, 50 mM inorganic phosphate) for all ligands. Circular dichroism in the far-UV region (190-250 nm) indicates no change in secondary structure on binding to the apoprotein. In the spectral region of 250-310 nm relatively large changes occur, indicating changes in the environment of the tyrosine and tryptophan residues. The single tryptophan residue shows a three-exponential decay of its fluorescence in both the apoprotein and the holoprotein. Radiationless energy transfer also occurs from the tryptophan to the bound ligand, especially evident with 7-oxolumazine. We have designed a new method for evaluation of the rate constant of energy transfer by measuring the (picosecond) rise time of the acceptor fluorescence. The anisotropy decay of the tryptophan residue shows two correlation times, a short one (phi approximately equal to 0.4 ns) representing rapid but restriced oscillation of this residue and a longer one (phi 2 = 5-7 ns, 20 degrees C) representing the motion of a larger segment of the protein.     

Effect of serotonin on proliferating and resting cells in culture

The influence of exogenous serotonin on cell division of L929 and L-41 cell strains has been investigated under various conditions of cell growth in culture (the incubation either in 10% serum medium without changing the medium, or in the medium with 0.5% serum). The data obtained show that serotonin in physiological concentration (10(-7) M) stimulates proliferation of resting cells. In proliferating cells, compared to resting ones, the sensitivity to exogenous amine appeared statistically non-significant. Exogenous serotonin is suggested to be a proliferating stimulus for resting cells.     

Activation of respiration in liver mitochondria by catecholamines]

Catacholamines activate in vivo and in vitro the rat liver mitochondria respiration (VO2) at high piruvate, 2-oxoglutarate and succinate concentrations. The effect was equally characteristic of free oxidation (state 4), phosphorylation (state 3), and even of VO2 uncoupled by DNP. EDTA and bovine serum albumin addition failed to eliminate the effect of the oxidoreductases activation by catecholamines.