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31.
The effect of UV light (lambda = 254 nm) on calf thymus DNP at low ionic strengths was studied. It was found that at the irradiation doses used the protein in the DNA-protein complex increases as the irradiation dose rises. Thermal treatment and acid hydrolysis resulted in a predominant release of histones H3 and H1 from the complex. Data from liquid high performance chromatography, amino acid analysis, thin-layer chromatography point to the induction by UV-light of a thymine-lysine bond, whose formation involves DNA thymines and histone lysine residues, predominantly H3 and H1 fractions. 相似文献
32.
Using two-dimensional thin-layer chromatography, the effect of serotonin on the yield of thymine dimers and on cleavage of the N-glycosidic bond in the DNA irradiated with ultraviolet (UV) light and X-ray was studied. Bound serotonin was shown to reduce the synthesis of UV-induced thymine dimers but had no effect on the number of X-ray-induced breaks in the N-glycoside bonds in thymidine residues. The data obtained are discussed in terms of the mechanisms of serotonin involvement in the photoprotection of yeast cells from the lethal action of UV and X-ray irradiations. 相似文献
33.
J Markussen I Diers A Engesgaard M T Hansen P Hougaard L Langkjaer K Norris U Ribel A R S?rensen E S?rensen 《Protein engineering》1987,1(3):215-223
It has previously been found that insulins, to which positive charge has been added by substitutions in position B30, thus raising the isoelectric point towards pH 7, had a prolonged action when injected as slightly acidic solutions because such derivatives crystallize very readily upon neutralization. Positive charge has now been added by substituting the B13 and A17 glutamic acid residues with glutamines and B27 threonine with lysine or arginine. These substitutions were introduced by site-specific mutagenesis in a gene coding for a single-chain insulin precursor. By tryptic transpeptidation the single-chain precursors were transformed to the double-chain insulin structure, concomitantly with incorporation of residue B30. Thus insulins combining B13 glutamine, A17 glutamine and B27 lysine or arginine with B30 threonine, threonine amide or lysine amide were synthesized. The time course of blood glucose lowering effect and the absorption were studied after subcutaneous injection in rabbits and pigs. The prolonged action of B30-substituted insulins was markedly enhanced by B27 lysine or arginine substitutions and by B13 glutamine. The B27 residue is located on the surface of the hexamer, so a basic residue in this position presumably promotes the packing of hexamers at neutral pH. The B13 residues cluster in the centre of the hexamer. When the electrostatic repulsive forces from six glutamic acid residues are abolished by substitution with glutamine, a stabilization of the hexamer can be envisaged.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
34.
I P Grigor'ev A A Neokesari?ski? 《Biulleten' eksperimental'no? biologii i meditsiny》1986,102(9):288-289
The effects of different concentrations of L-ascorbic acid (Asc) on Na+-dependent binding of 3H-GABA and 3H-DL-glutamic acid to rat brain cortical synaptosomes were studied. Asc, at a concentration nearly equal to brain extracellular one (3 X 10(-4) M), had no effect on specific and nonspecific 5H-GABA binding. At higher concentrations (10(-3) M) Asc strongly inhibited, and at lower concentrations (10(-6) M) considerably stimulated 3H-GABA binding. At a concentration of 10(-5)-10(-3) M Asc tended to decrease 3H-DL-glutamic acid binding. 相似文献
35.
D G Astaf'ev I V Maianskaia A K Akatov A N Maianski? 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(7):48-51
In investigations based on the use of a highly sensitive test system permitting the detection of normal human antibodies to S. aureus peptidoglycan, the antigenic relationships between the peptidoglycans of S. aureus and other representatives of the genus Staphylococcus have been studied. Among other staphylococcal species, S. simulans, S. xylosus, S. hyicus, S. cohnii, S. hyicus s. s. chromogenes have been found to possess peptidoglycans most closely related to S. aureus peptidoglycans, while S. warneri and S. epidermidis peptidoglycans have proved to be least closely related to it. 相似文献
36.
ESR spectra of gamma-irradiated and frozen at 77 K human oxyhemoglobin and partially denaturated methemoglobin solutions were analysed. The quartet signal ascribed to the anion-radical of proximal histidine was shown to dominate in the spectra of both solutions. The spectra of methemoglobin solution irradiated with relatively small doses have an intensive singlet ascribed to the stabilized electron. The formation mechanism of free radicals is discussed. 相似文献
37.
Two forms of a carbon monoxide-binding cytochrome were found to exist in CaCl2-precipitated microsomal subfractions of human placental homogenates at term. These exhibited absorption maxima at wavelengths of 450 nm and 421–432 nm. Conversion of P-450 to the degradation product could be prevented by resuspension of the microsomes in buffered solutions containing 20% glycerol and 10?4M dithiothreitol. Solubilization of such resuspended microsomes with sodium cholate could be effected with minimal degradation. The solubilized pigment then could be partially purified by differential fractionation with ammonium sulfate. The partially purified cytochromes did not appear to bind desmethylimpramine but did bind aniline and nicotinamide to yield atypical type II difference spectra with maxima at 435 nm and minima at 416 nm. A type I difference spectrum could be elicited with androstenedione and a spectral dissociation constant (KS) of 4.7×10?8M was obtained. Androstenedione also appeared to effectively prevent the binding of carbon monoxide to the cytochrome. 相似文献
38.
Interaction between cytotoxin of the Central Asia cobra venom and dimiristoylphosphatidylcholine bilayer depending on its phase state was studied by ESR with spin label. A conclusion can be drawn that the efficiency of cytotoxin effect on the membranes depends on their phase state. Cytotoxin molecules are incorporated into myophile region of the bilayer, only if the latter is in the liquid crystal state. The interaction between cytotoxins and lipids of the bilayer in a gel state is in the main conditioned by electrostatic forces. 相似文献
39.
40.
Summary Pleiotropic mutants of Serratia marcescens have been isolated. They synthesize greater quantities of the bacteriocin marcescin A and exocellular lipase and exhibit higher rates of spontaneous induction of prophage than does the wild-type strain. These mutants were found to contain more marcescin A plasmid DNA than the parent strain and, furthermore, this increase in plasmid DNA was observed to be proportional to the increase in synthesis of marcescin A. From these results it is proposed that the mutation functions via a gene-dosage effect (at least in the case of bacteriocin synthesis) and causes an elevated synthesis of bacteriocin plasmid DNA.A preliminary report of this work was presented to the 1972 Summer Meeting of the Gesellschaft für Physiologische Chemie held in Bochum, Germany (Timmis and Winkler, 1972). 相似文献