Segmental flexibility of single-, double-, and triple-stranded polyribonucleotides from the data of spin label method. Formation of the triple-stranded poly(A.A.U) polynucleotide helix

Segmental mobility dynamic peculiarities of poly(U), poly(A) and poly(C) synthetic polymers and their complexes were investigated by spin-label method. Imidazolide spin-label was introduced into 2'-oxi-groups of polymer ribose in correlation: one spin-label on 18-20 bases. Formation of complexes was observed by ESR spectra at two pH: 4.2 and 7.2. Segmental mobility of only single strand spin-labelled polymer segment and in the complex was evaluated by measuring rotational correlation time (tau) determined by dependence of distances between outer wide extrema in ESR spectra from solvent viscosity at different temperatures. It turned out that correlation time tau of single strand structures in a high degree depend on pH and temperature. For three strand structures abrupt increase of tau because of appearance of rigidity was observed. It is possible to evaluate part of triple complexes poly(U.A.A) and poly(U.U.A) existing in dynamic equilibrium depending on pH and temperature by the form of outer wide extrema. Adding of dye to complex of poly(U).poly(A) causes an increase of rigidity of the supermolecular structure. Quantitative characteristics of formed complexes were obtained by simulation of ESR spectra on computer.     

Crystal structure of thermitase and stability of subtilisins

Crystal structure of thermitase, a serine proteinase from Thermoactinomyces vulgaris, has been determined by X-ray diffraction at 1.4 A resolution. The atomic model of thermitase refined to an R-factor of 0.149 contains 1997 protein atoms, 182 water molecules and 2 Ca2+ ions. The tertiary structure of thermitase is similar to that of subtilisin BPN'. The greatest variations are connected with insertions and deletions in the amino acid sequence, which are located on the surface of the molecule. Higher thermostability of thermitase can be explained in terms of the three-dimensional structure. The Ca2+ ions, bound to the protein molecule, as well as the ionic and hydrophobic interactions are supposed to give the main contribution to the stabilization of the structure.     

Isolation and characterization of plasma membrane-associated cortical granules from sea urchin eggs

Cortical granules, which are specialized secretory organelles found in ova of many organisms, have been isolated from the eggs of the sea urchins Arbacia punctulata and Strongylocentrtus pupuratus by a simple, rapid procedure. Electron micropscope examination of cortical granules prepared by this procedure reveals that they are tightly attached to large segments of the plasma membrane and its associated vitelline layer. Further evidence that he cortical granules were associated with these cell surface layers was obtained by (125)I-labeling techniques. The cortical granule preparations were found to be rich in proteoesterase, which was purified 32-fold over that detected in a crude homogenate. Similarly, the specific radioactivity of a (125)I-labeled, surface glycoprotein was increased 40-fold. These facts, coupled with electron microscope observations, indicate the isolation procedure yields a preparation in which both the cortical granules and the plasma membrane-vitelline layer are purified to the same extent. Gel electrophoresis of the membrane-associated cortical granule preparation reveals the presence of at least eight polypeptides. The major polypeptide, which is a glycotprotein of apparent mol wt of 100,000, contains most of the radioactivity introduced by (125)I-labeling of the intact eggs. Lysis of the cortical granules is observed under hypotonic conditions, or under isotonic conditions if Ca(2+) ion is present. When lysis is under isotonic conditions is induced by addition of Ca(2+) ion, the electron-dense contents of the granules remain insoluble. In contrast, hypotonic lysis results in release of the contents of the granule in a soluble form. However, in both cases the (125)I-labeled glycoprotein remains insoluble, presumably because it is a component of either the plasma membrane or the vitelline layer. All these findings indicate that, using this purified preparation, it should be possible to carry out in vitro studies to better define some of the initial, surface-related events observed in vivo upon fertilization.     

Synthesis of ATP and free radicals in an aqueous solution, containing NADH, riboflavin, ADP and inorganic phosphate

pH-dependence of initial (admixture) adenosine triphosphate (ATP) changes (ATP synthesis and hydrolysis) was studied for aerated and deaerated aqueous solutions during the incubation of adenosine diphosphate (ADP) and inorganic phosphate (Pi) in the presence of reduced nicotinamide adenine dinucleotide (NADH) and riboflavin (Rf). The preferential pH regions were indicated both for ATP synthesis and ATP hydrolysis (pH less than pH 5.4, 5.9 divided by pH 6.5 and pH greater than 6.6, pH 5.5 divided by pH 5.8 respectively). 'Free radical content measurements were paralleled by ESR technique. On the basis of the obtained results it was assumed that a part of ESP signal attributed to ADP radicals was increased during ATP synthesis.     

Changes in rigidity of the polymeric chain of the lambda-phage DNA in aqueous solutions with low ionic strength over the pH range 4-9.5

It was shown that the decrease in the rigidity (persistent length) of phage lambda DNA, revealed previously by laser correlation spectroscopy, occurs in an aqueous solution at concentrations of sodium salts less than 10(-2) M in the pH range 4-9.5. DNA coils of anomalously small size (approximately twofold less than the size reported by other authors) are formed. The formation of these coils is likely to be due to the separation of "normal", i.e., rigid DNA coils into two phases, which occurs as the concentration of sodium salts decreases to 1.5 x 10(-3) M and pH of the solution decreases to 4. The phase of small-size (nonrigid) coils makes the major contribution to the scattering spectra. The phase of large-size coils disappears at pH 9.5. As pH increases, the size of small coils increases. The occurrence of coils of anomalously small size was registered by another method, quick precipitation. It is assumed that the phase separation of coils is related to the structural features of water.     

Effect of pineal peptide on parameters of the biological age and life span in mice

Female CBA mice were injected with s.c. synthetic tetrapeptide Epithalon from a 6-month age until death. The drug failed to affect the body weight or food consumption, physical activity or behavioural parameters. However, it slowed down the age-related switching off of the estrus function, decreased body temperature, decelerated free redical processes, prolonged the mice life span with an accompanying drop in spontaneous tumour incidence.     

Influence of tenotomy on posttetanic responses of the rat fast and slow muscle

The effect of two weeks of tenotomy on posttetanic isometric contractile responses of the rat fast: Extensor digitorum longus and slow: soleus muscles was studied in experiments on isolated muscle preparations. Direct tetanic stimulation (100 impulses, 50 Hz) increased the force of contractions by 20-25% (p < 0.05) of both, control and tenotomized fast muscles. Identical to above tetanic stimulation of control, slow muscle resulted in posttetanic depression, a decrease in the amplitude of contractile responses. Tenotomized slow muscles did not develop posttetanic depression. Caffeine (4 mM) increased and dandrolene (10 microM) decreased the force of unitary and tetanic contractions of control and tenotomized muscles. Neither drug, however, affected development of posttetanic phenomena in ether fast or slow muscles. The fact that in extensor digitorum longus, posttetanic potentiation is preserved for at least forty days of tenotomy but disappears after only 2 weeks of denervation suggests important role of neurotrophic influences in regulation of posttetanic responses of fast muscles.