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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
Mol Biol (Mosk)
PMID:[Modification of the retina photoreceptor membranes and temperature stability of rhodopsin]. 73 88

Ca2+-entry into intact red cells containing [32P]-ATP increases the phosphorylation of the 150 000 dalton polypeptide of the membrane. This phosphorylation occurs even in Mg2+-depleted red cells. Extracellular lanthanum applied during ATP-depletion further increases the Ca2+-induced phosphorylation. In fragmented membranes or resealed insideout vesicles (IOVs) membrane bound Mg2+ is sufficient to catalyze the phosphorylation of spectrin 2 and Band 3 polypeptides with low concentrations (less than micron of [32P]-ATP. In Ca-EDTA buffers one single polypeptide is phosphorylated which is located in the 150 000 molecular weight region. KmCa for phosphorylation is much lower (0.2 micron) than for active Ca2+ transport (40 micron) in IOVs. Lanthanum induced phosphorylation (up to 250 micron Lafree) is significantly greater than Ca2+-induced phosphorylation. Hg2+ inhibits both Ca2+ and La3+ induced phosphorylation. Ca2+-induced labelling can be rapidly "chased" by unlabelled ATP+Mg2+, but not with EGTA+Mg2+. Dephosphorylation in Ca2+ phosphorylated membranes and IOVs is significantly inhibited by La3+. It can be concluded that the mechanism of La3+ and Hg2+ inhibition of the Ca2+ pump is different in intact cells and isolated membranes or Iovs.
Mol Cell Biochem 1978 Dec 22
PMID:Phosphorylation of the Ca2+ pump intermediate in intact red cells, isolated membranes and inside-out vesicles. 74 97

The secondary structure of DNA is known to be largely determined by the kind of counterion bound to it. We have used the X-ray diffraction method to study the structure of magnesium and lithium salts of T2 phage DNA in oriented fibres. The structural behaviour of this glucosylated DNA in the form of magnesium and lithium salts was shown to be identical to the behaviour of the same salts of "normal" calf thymus DNA throughout the studied range of relative humidities (44-95%). However these two DNAs in the form of sodium salt are known to behave quite differently. One can presume that Mg2+ and Li+ influence the structural behaviour of double-stranded DNA so effectively as to be able to "ignore" the fact that T2 phage DNA contains glucoside residues. The results of this work and the already known facts concerning the structure of DNA in the form of various cation salts (in solution and in "solid" fibres) indicate that the structural behaviour of double-stranded DNA is mainly determined by the cation located in the region of the narrow groove of the double helix. If cations are graded according to the efficiency of their influence on the structural behaviour of DNA in fibres, the scale will coincide with that of their DNA-binding strength in water solution, that is: Mg2+ greater than Li+ greater than Na+ greater than K+ greater than Rb+. A qualitative consideration of electrostatic interaction between the cations and the negatively charged DNA strands leads one to suppose that this interaction must obstruct the transition of individual DNA molecules from the B-form to the A-form. Aggregation of self-aggregation of DNA molecules is presumed necessary to enable them to adopt the A-conformation.
Mol Biol (Mosk)
PMID:[Investigation of the structure of magnesium and lithium salts of T2 phage DNA by the method of x-ray diffraction. The possible mechanisms of the participation of cations in the structural transformation of double-stranded DNA]. 74 8

Binding of oxytetracycline to E. coli ribosomes was studied by equilibrium dialysis. The results are consistent with the existence of two classes of binding sites for the antibiotic on ribosomes having different reactivities. There is one strong binding site as well as about 500 weak ones. The association constant for strong complexes is about 10(3) times greater than the value for weak ones. Oxytetracycline and tetracycline bind to ribosomes as magnesium chelates. Increase of the concentration of Mg2+ leads to the formation of two types of magnesium chelates of the antibiotic: chelate 1 which is formed at a relatively low concentration of Mg2+ and has a stiochiometry 1:1, and chelate 2 which probably corresponds to the attachment of second ion to the antibiotic molecule. The strong binding of oxytetracycline to ribosomes prevents the template dependent association of aminoacyl-tRNA with ribosomes. However, no changes in the extent of the antibiotic binding were found upon addition of aminoacyl-tRNA, poly(U) and chloramphenicol to oxytetracycline-ribosome complexes. It has been suggested that inhibiting effect of oxytetracycline on the protein synthesis involves an allosteric mechanism.
Mol Biol (Mosk)
PMID:[Oxytetracycline binding to E. coli ribosomes]. 77 91

Conformational transitions in several individual tRNAs (tRNAMetf, tRNAPhe from E. coli, tRNAVal1, tRNASer, tRNAPhe from yeast) have been studied under various environmental conditions. The binding isotherms studies for dyes-tRNA complexes exhibited similarities in conformational states of all tRNAs investigated at low ionic strength (0.01 M NaCl). By contrast, at high ionic strength (0.4 M NaCl or 2 X 10(-4) M Mg2+) a marked difference is found in structural features of tRNAMetf as compared with other tRNAs used. The tRNAMetf is the only tRNA species that does not reveal the strong type of complexes with ethidium bromide, acriflavine and acridine orange.
Mol Biol Rep 1976 Jul
PMID:Conformational peculiarities of tRNAMetf from E. coli as revealed by fluorescent methods. 78 33

The magnesium dependence of the Escherichia coli ribosomal subunits association has been investigated by the stopped-flow technique using isolated 30S and 50S particles depleted of polyamines and any initiation factor. Binding of the fluorescent probe bis(8-anilino-1-naphthalenesulfonate) to the ribosomal proteins occurs through biphasic kinetics. A dark reaction corresponding to a very rapid, reversible complexation of the dye molecule is followed by a slow photochemical reaction that gives rise to irreversible addition of the probe. Only the 30S subparticle exhibits a magnesium-dependent conformational change from the kinetic analysis of the dark reaction. The 70S formation kinetics are limited by a conformational change of the 30S subunit if this particle is depleted of Mg2+ (1 mM Mg2+/50 mM K+), while its activated structure is restored by incubation with 8 mM Mg2+/50 mM K+. No rate-limiting conformation rearrangement of the 50S subunit could ever be evidenced. The Mg2+ dependence of the association kinetics of preactivated ribosomal particles is satisfactorily explained by electrostatic effects and/or formation of salt bridges, in agreement with the results of Wishnia and co-workers (Wishnia, A. Boussert, A., Graffe, M., Dessen, P., and Grunberg-Manago, M. (1975), J. Mol. Biol. 93, 499). Equilibrium studies indicate that the ribosomal preparations we used are of B type, according to Debey et al. (Debey, P., Hui Bon Hoa, G., Douzou, P., Godefroy-Colburn, T., Graffe, M., AND Grunberg-Manago, M. (1975) Biochemistry 14, 1553). The addition of spermidine results in a drastic fall of the need of Mg2+ for association, but it does not allow conversion of B-type particles into A-type ones at 25 degrees C. In addition to that, some 30S-bound spermidine appears to be involved directly in the coupling reaction.
 ...
PMID:Magnesium dependence of the association kinetics of Escherichia coli ribosomal subunits. 78 63

A method for the isolation of highly active Escherichia coli ribosomal subunits has been described and used to obtain 30S subunits, which are fully active in the cistron-specific binding of tRNA, and reassociated 70S ribosomes, which are at least 35% active in the synthesis of polypeptides. The dissociation constants (Kd) of the 30S-poly(U)-tRNAPhe complex, which proved to be practically identical for tRNAPhe in the deacylated and aminoacylated forms, as well as for the chemically synthesized peptidyl-tRNA, have been measured. Changes in the binding conditions (temperatures from 0 to 30 degrees, Mg2+ concentrations from 20 to 5 mM, and NH4+ concentrations from 200 to 50mM) have a significant effect on the value of Kd without altering the number of active 30S subunits. It has been shown that the codon-specific binding of tRNA to the 30S subunits is completely reversible. The 30S subunits are not only not inactivated after a single act of binding of a tRNA molecule, but are capable of undergoing this process repeatedly without any appreciable loss in activity.
Mol Biol (Mosk)
PMID:Isolation and study of some properties of the highly active 30S and 50S Escherichia coli ribosomal subunits. 79 55

The enzyme which catalyses template independent synthesis of polydeoxynucleotides from deoxynucleoside diphosphates was separated from E. coli DNA polymerase I by DEAE-cellulose chromatography followed by ultrafiltration through the M-50 Amicon filter. The ultrafiltration data indicate that the molecular weight of the enzyme is not higher than 50,000. The enzyme is not able to use deoxynucleoside triphosphates, ribonucleoside di- or triphosphates as substrates for the polymerization. The reaction of template independent polymerization proceeds with a lag period varying from 2 to 20 hours (for different preparations of enzyme) and is activated by Mg2+ (the optimal concentration 1-2 . 10(-3) M). The pH optimum of the reaction is at 8.5. The optimal concentration of deoxyribonucleoside diphosphates is 10(-3) M, and its increase strongly inhibits polymerization. The enzyme was supposed to be called deoxynucleoside diphosphate: olygonucleotide deoxynucleotidyltransferase (catalyzing polymerization without template). The presence of the enzyme in the preparations of E. coli DNA-polymerase I can explain the ability of the latter to catalyze the untemplated synthesis of poly dG : poly dC.
Mol Biol (Mosk)
PMID:[Separation of the enzyme catalyzing polymerization of deoxyribonucleoside diphosphates from preparations of E. coli DNA-polymerase I]. 80 82

Conformational transitions in tRNAfMet E. coli the initiator tRNA in bacterial systems and in some other individual tRNAs have been studied as a function of monovalent and divalent ion concentrations. By measuring the extent of energy transfer between dye molecules adsorbed on tRNAs and by study of adsorption isotherms of dyes on tRNAs conclusion has been drawn about the similarity of conformational state of all tRNAs studied at low ionic strength (mu 0.01). A conformational change in tRNA, produced by an addition of Mg2+ and Na+ ions results in more than two fold decrease of the strong binding sites for dyes. A marked difference in the adsorption properties of tRNAfMet in comparison with other investigated tRNAs were found. The tRNAfMet was the only tRNA species that did not form the strong type of complexes with dyes at high ionic strength
Mol Biol (Mosk)
PMID:[Conformational transitions in tRNA fMet from E. coli induced by monovalent and divalent ions]. 80 88

The enzymes involved in host-controlled modification and restriction by Bacillus subtilis strain N were detected in cell free extracts. In the presenct of Mg2+ the N-specific endonucleases cleaved unmodified DNA but did not attack phi-105C. N DNA carrying N-specific modification. The restriction endonuclease required neither SAM nor ATP for its activity. The N-specific modification enzyme was active only in the presence of SAM, indicating that modification in this syteem is a methylation of DNA.
Mol Gen Genet 1975 Jul 10
PMID:In vitro modification and restriction of phage phi-105c DNA with Bacillus subtilis N cell-free extract. 80 94


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