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At least 1,027 records · Page 57Linked to original sources
PubMed1992

Cartilage matrix proteins. An acidic oligomeric protein (COMP) detected only in cartilage.

An Mr = 524,000 oligomeric protein was isolated from bovine cartilage and designated COMP (Cartilage Oligomeric Matrix Protein). The protein is composed of disulfide-bonded subunits with an apparent Mr of 100,000 each. It is markedly anionic, probably due to its high contents of aspartic acid and glutamic acid, as well as to its substitution with negatively charged carbohydrates. COMP was found in all cartilages analyzed, but could not be detected in other tissues by enzyme-linked immunosorbent assay of guanidine HCl extracts. Within a given cartilage, COMP shows a preferential localization to the territorial matrix surrounding the chondrocytes.

Amino Acids↗
PubMedDate not supplied

[The component analysis of tryptophan fluorescence spectra of melittin during its oligomerization].

The oligomerization of melittin with increasing ionic strength and protein concentration was investigated using the methods of decomposition of its tryptophan fluorescence spectra into "elementary" log-normal components. At high ionic strength (up to 2 M KCl), the emission spectra of tetrameric melittin are well described as the sum of two log-normal components, suggesting the presence of tryptophan residues in two sorts of environment with greatly differing polarity. Measurements of fluorescence spectra by iodide showed that these two spectral components possess different Stern-Volmer constants, that is, the tryptophans emitting them have different solvent accessibility, which does not correlate with the crystallographic structure of tetrameric melittin. Moreover, in the oligomerization transition induced by ionic strength, the tetrameric intermediate is formed, which has log-normal spectral components with relative contributions differing from those in 2 M KCl.

Melitten↗
PubMed1991

[Artificial oligomerization of enzymes--a new way of regulating their catalytic activity in reversed micellar systems].

Comparative studies were carried out in the catalytic activity regulation of native alpha-chymotrypsin and its artificially produced hexameric form as an example of non-dissociating oligomeric enzyme (covalently cross-linked by means of succinimidyl-3-(2-pyridylthiopropionate] in the Aerosol OT reversed micelles in octane. Native (monomeric) alpha-chymotrypsin exhibits maximal catalytic activity in the reversed micelles at the hydration degree w0 = 10, when the radius of the micelle inner cavity is equal to the radius of the alpha-chymotrypsin globule. For the alpha-chymotrypsin hexamer, optimum is observed at w0 = 45, with the inner micellar cavity radius (r = 68 A) being approximately equal to the radius of the sphere surrounding the octahedral combination of the six monomeric alpha-chymotrypsin molecules (r = 61 A). Thus, construction of the corresponding oligomeric structures is made easy, with the optimal catalytic activity in a preset range of the hydration degrees.

Animals↗
PubMed1991

Oligomeric nature of transmembrane glycoproteins of HIV-2: procedures for their efficient dissociation and preparation of Western blots for diagnosis.

Western blot (WB) analysis of various strains of HIV-2 indicated that transmembrane glycoprotein (TMP) of HIV-2 exists as trimers. These trimers have molecular weights and electrophoretic mobilities in the region of the major external glycoprotein, gp120, resulting in WB misidentification during diagnosis. A simple and rapid procedure was developed using trichloroacetic acid (TCA) to efficiently dissociate oligomeric forms of the TMP to monomers prior to the preparation of WB. This procedure permitted the unambiguous identification of antibodies to gp120 and to the TMP. Use of HIV-2 WB strips without any oligomeric forms of the TMP demonstrated (1) that cross reactivity of HIV-1-positive specimens on HIV-2 WB was mainly directed to Gag and Pol proteins, with some reactivity to gp36/gp41 TMP, but none to gp120; (2) that these strips can substantially reduce the number of specimens falsely identified as dually (HIV-1 and HIV-2) reactive; and (3) that HIV-2-positive specimens reacted to viral gp120 in a strain-specific manner, demonstrating high antigenic variation in this glycoprotein. It is recommended that this general procedure of viral protein dissociation be used for HIV-2 WB preparation.

Blotting, Western↗
PubMed1989

Protein kinase C inhibition of the epidermal growth factor receptor tyrosine protein kinase activity is independent of the oligomeric state of the receptor.

Treatment of A431 human epidermoid carcinoma cells with 4-phorbol 12-myristate 13-acetate (PMA) causes an inhibition of the high affinity binding of epidermal growth factor (EGF) to cell surface receptors and an inhibition of the EGF receptor tyrosine protein kinase activity. The hypothesis that PMA controls EGF receptor function by regulating the oligomeric state of the receptor was tested. Dimeric EGF receptors bound to 125I-EGF were identified by covalent cross-linking analysis using disuccinimidyl suberimidate. Treatment of cells with PMA in the presence of 20 nM 125I-EGF caused no significant change in the level of labeled cross-linked monomeric and dimeric receptor species. Investigation of the in vitro autophosphorylation of receptor monomers and dimers cross-linked with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide demonstrated that the treatment of cells with PMA caused an inhibition of the tyrosine phosphorylation of both monomeric and dimeric EGF receptors. We conclude that the inhibition of the EGF receptor tyrosine protein kinase activity caused by PMA is not associated with the regulation of the oligomeric state of the EGF receptor.

Carcinoma, Squamous Cell↗
PubMedDate not supplied

[Simulation of the kinetics of oligomeric enzymes as illustrated by phosphofructokinase. I. General analysis of experimental data and the choice of an adequate model].

On the example of complex allosteric kinetics of phosphofructokinase from human erythrocytes we analysed the applicability of the Monod-Wyman-Changeux and association--dissociation models to the unified description of the kinetics of the oligomeric enzymes. It was shown that these models were not sufficient to construct an adequate phosphofructokinase model. We propose to use the unidimensional Izing model for this purpose. It was analysed in the monosubstrate case for the high enzyme concentration range. The ways to generalize the Izing model as the basis of the universal model for the oligomeric enzyme's kinetics were analysed.

Adenosine Triphosphate↗
PubMedDate not supplied

[Kinetic model of the action of oligomeric enzymes using phosphofructokinase as an example. II. General formulation of the hierarchical model].

A general approach is suggested to describe the steady-state kinetics of the oligomeric enzymes on the base of the generalized statistical Ising model. Detailed analysis is given for the case of a oligomeric enzyme with a hierarchical supramolecular organization. A protomer of this enzyme composed of several equivalent subunits represents the quarternary level of structure. In their turn the finite or infinite number of protomers is associated into a oligomer thus creating a new "quinternary" level of the enzyme organization. The model accounts for the ligand-induced homotrophic cooperative interactions: firstly, between the neighbouring protomers and secondly, between the subunits of the same protomer. The influence of protomer conformation on the subunit state and the cooperativity induction caused by two-ligand binding are also taken into consideration. Monod-Wyman-Changeux's and Koshland's models are shown to be special limit cases of the suggested general theory.

Enzymes↗
PubMed1986

[The role of oligomeric structure in the functioning of D-glyceraldehyde-3-phosphate dehydrogenase].

The review summarizes the results of a study on the functional role of subunit interactions in a tetrameric glyceraldehyde-3-phosphate dehydrogenase molecule. A conformational asymmetry preexistent in the apoenzyme was shown to be detectable with the use of fluorescent cationic probes. Experimental evidence is presented which points to an interaction of the enzyme active centers in the course of productive E-acyl-NADH complex formation in the forward reaction. The matrix immobilized oligomeric and subunit forms of the enzyme were used to demonstrate that the quaternary structure is not a prerequisite for the catalytic activity. Due to subunit interactions within the oligomeric enzyme molecule the functioning of a monomer is under the control exerted by the neighbouring subunits. An association of monomers into a dimer is sufficient to create a cooperative system; the mutual influence of subunits becomes more complex in a trimeric and a tetrameric enzyme species. An isolated dimer exhibits the effect of half-of-the-sites reactivity and catalytic cooperativity of the active centers. Both the tetrameric and dimeric enzyme forms probably catalyze the reaction of 1,3-diphosphoglycerate reductive dephosphorylation via a mechanism of the flip-flop type. The catalytic cooperativity of the enzyme active centers can be controlled by some factors of the intracellular environment (e.g., by protein-protein interactions with a functionally related enzyme). Thus, the role of subunit cooperativity in the glyceraldehyde-3-phosphate dehydrogenase molecule is suggested to constitute one of the mechanisms of regulation of the enzyme functioning.

Animals↗
PubMed1987

[Determination of isoelectric points of oligomeric forms of mitochondrial creatine kinase].

Using isoelectrofocusing in three pH gradients differing in the initial pH value of the ampholyte gel mixture and in gradient pH range, the isoelectric points for the dimeric and octameric forms of mitochondrial creatine kinase from bovine heart and pigeon breast muscle were determined. The isoelectric points for the dimer and octamer are equal to 9.67 +/- 0.01 and 8.93 +/- 0.05 for the heart enzyme and to 9.56 +/- 0.08 and 8.91 +/- 0.23 for the skeletal muscle enzyme. The correctness of identification of the oligomeric forms of mitochondrial creatine kinase was confirmed by ultracentrifugation in a sucrose density linear gradient. Since creatine kinase is known to bind to mitochondrial membrane cardiolipin by electrostatic forces, it can be assumed that both oligomeric forms of the enzymes can bind to the membranes. However, the properties of the creatine kinase dimer suggest its greater ability to bind to mitochondrial membranes.

Animals↗
PubMedDate not supplied

[Oligomerization of phenylalanine hydroxylase during its activation with phenylalanine].

Activated and nonactivated forms of phenylalanine hydroxylase varied in the activity within the first minutes of the reaction initiated by means of a synthetic coenzyme 6,7-dimethyl-5,6,7,8-tetrahydropteridine. In activation of the enzyme by phenylalanine the degree of its oligomerization was altered. As shown by chromatography and ultracentrifugation nonactivated enzyme was a dimer with molecular mass 130,000 daltons, whereas the activated form was found to be tetramer of 260,000 daltons. H and L subunits of phenylalanine hydroxylase were equally important in organization of the tetramer. Activation of phenylalanine hydroxylase altered the enzyme affinity to hydroxyapatite. Thus, allosteric activation of phenylalanine hydroxylase occurred due to the enzyme oligomerization.

Animals↗
PubMed1977

[Reaction of local myocardial blood flow in non-anesthetized dogs and anesthetized cats to the oral and parenteral administration of a Crateagus fraction (oligomere procyanidines)].

Local blood flow in the myocardium of the left ventricle in unanesthetized dogs was measured by chronically implanted heat-conduction probes. Oral administration of a fraction of Crataegus (oligomere procyanidines) led to a significant rise in blood flow for several hours depending on the dose, the highest increase reaching an average value of about + 70% of the resting flow. In dogs regularly fed with this substance for a longer period of time, a rising tendency of the matutinal resting values of myocardial blood flow towards a maximum was seen. Intravenous application of oligomere procyanidines in anesthetized cats led to a dose-dependent increase in myocardial blood flow for several minutes and a slight decrease in arterial blood pressure.

Administration, Oral↗
PubMed1984

[Molecular organization of cholesterol-hydroxylating cytochrome P-450 from adrenal cortex mitochondria. Chemical modification with bifunctional reagents in the study of oligomeric forms].

The molecular organization of adrenocortical cytochrome P-450scc has been investigated using chemical modification with bifunctional imidates. The oligomeric organization of cytochrome P-450scc in solution has been shown. The application of dimethyl-3,3'-dithiobispropioimidate and subsequent cleavage of the modified products by reducing agents revealed the presence of two types of intramolecular cross-links: "short" at the distance of 3,0 A between the amino groups of lysine residues and "long" ones at a distance of 11,9 A. The analysis of the products, obtained by limited proteolysis of the oligomeric forms of the cross-linked cytochrome P-450, by two-dimensional electrophoresis has shown that the cross-links are formed between the functional domain (fragment F1) and domain responsible for the interaction with the phospholipid membrane (fragment F2). A model for cytochrome P-450scc molecular organization has been suggested on the basis of the obtained results.

Adrenal Cortex↗
PubMedDate not supplied

[A model of oligomeric enzymes explaining stepwise kinetic curves].

The complex kinetics of some oligomeric enzymes has been analysed. For interpreting such kinetics a theoretical model of an oligomeric enzyme is suggested, which is a modification of the "flip-flop" mechanism considered by Lazdunski et al. in 1971. Using our model, one can qualitatively interpret stepwise kinetic curves, i.e. the curves with few intermediate plateaus. Such curves are known from literature but have not exhaustively been explained. It is supposed that the enzyme kinetic curves can sometimes be of non-differential functions. The model used can also be applied to the kinetics of polyenzyme complexes.

Catalysis↗
PubMed1980

[Factors causing oligomerization of wall-eyed pollock rhodopsin before and after solubilization by sodium dodecyl sulfate].

Using SDS-electrophoresis, it was shown that the addition of sodium ions to the solubilization medium causes oligomerization of wall-eyed pollock rhodopsin. Oligomerization is also caused by solubilization of the wall-eyed pollock rod outer segments by sodium cholate (deoxycholate), by changes in SDS concentration as well as by an increase of protein content in the solubilization mixture, freezing of solubilizate and treatment of the rod outer segments by sodium borohydrate upon illumination. Possible causes of wall-eyed pollock rhodopsin aggregation are discussed.

Animals↗
PubMed1995

Characterization of the promoter region and oligomerization domain of H4 (D10S170), a gene frequently rearranged with the ret proto-oncogene.

PTC-1, the predominant form of PTC oncogene in human papillary thyroid carcinoma, encodes a fusion protein containing the N-terminus of H4 (D10S170) fused 5' to the ret tyrosine kinase domain. Accordingly, the PTC-1 expression is driven by the H4 gene promoter. Our study showed that H4 is expressed in various human tissues, including thyroid. Furthermore, we have localized the transcriptional start sites of H4 to a region 100 to 190 bp upstream of the translation initiation site (ATG) by primer extension assay, and the H4 promoter to a region within 259 bp upstream of the ATG site by luciferase assay. Interestingly, protein sequence analysis indicated a potential coiled-coil domain in the N-terminal region of H4. Indeed, oligomerization was demonstrated by an in vitro assay with recombinant proteins containing this region. As dimerization is considered to be a crucial step for receptor tyrosine kinase activation, we hypothesize that both unscheduled expression of ret tyrosine kinase and constitutive oligomerization of PTC-1 proteins are responsible for PTC-1 transforming activity in thyroid.

Base Sequence↗
PubMed1995

Oligomeric IgD augments and monomeric IgD inhibits the generation of IgG memory antibody responses in normal, but not in IgD-deficient, mice.

Dimeric or aggregated IgD causes augmentation of primary and secondary Ab responses in mice when injected a few days before or together with the primary dose of Ag. This effect is mediated by Th cells and seems to be linked to the up-regulation of receptors for IgD on CD4+ T cells. IgD-R cross-linking is needed for receptor up-regulation. Here we show that addition of monomeric IgD to dimeric or aggregated IgD blocks IgD-R up-regulation on T cells in vitro and in vivo, as well as their immunoaugmenting effect in vivo. More importantly, monomeric IgD injected 6 to 24 h before a primary Ag injection also inhibits 1) the up-regulation of IgD-R on T cells induced by Ag injection alone, and 2) the generation of IgG memory, as shown in the response to a second dose of Ag injected on day 10. These results suggest that IgD-R on T cells contribute to the T-B cell interaction involved in the priming for a secondary response. The augmenting effect of oligomeric IgD and the inhibiting effect of monomeric IgD on secondary Ab responses are not observed in IgD-/- (IgD-deficient) mice, although injection of oligomeric IgD leads to IgD-R up-regulation on T cells in these mice. These results indicate that IgD presented in the form of immune complexes, most likely on the surface of B cells, is a prerequisite for the immunoaugmenting effects exerted by IgD-R+ T cells. Thus, IgD is the only physiologic ligand for IgD-R on T cells.

Animals↗
PubMed1976

Biosynthesis of bacterial glycogen. Activator-induced oligomerization of a mutant Escherichia coli ADP-glucose synthase.

ADP-glucose synthase (EC 2.7.7.27) was purified to homogeneity from SG5-504, Aa mutant strain of Escherichia coli B. It had a molecular weight of approximately 2 X 10(5) and four identical subunits. In the presence of its allosteric activator, fructose-1-6-P2, the mutant enzyme formed oligomers with several times the tetramer molecular weight, as revealed by sedimentation equilibrium centrifugation, polyacrylamide gel electrophoresis, and gel filtration column chromatography. Enzyme purified from a wild type strain, AC70R1, did not exhibit the activator-induced oligomerization. Catalytically, the mutant enzyme had a 2-fold higher affinity for activator and a 2- to 3-fold lower affinity for the allosteric inhibitors 5'-adenylate and KH2PO4 than the wild type. The two enzymes appeared identical in subunit molecular weight, amino acid composition, COOH-terminal amino acid, and the first 27 residues of the NH2-terminal sequence. Subtle structural differences were revealed by chemical modification of specific residues. Compared to wild type, the mutant enzyme had 1 cysteine/subunit more accessible to modification by Ellman's reagent. SG5-504 enzyme was inactivated more slowly than AC70R1 enzyme by phenylglyoxal and by trinitrobenzenesulfonate. These results reflected an altered conformation of the SG5-504 enzyme molecule. The unique ability of it to oligomerize in the presence of activator may be the result of a single amino acid substitution.

Amino Acid Sequence↗
PubMed1993

Nucleolar protein B23: bacterial expression, purification, oligomerization and secondary structures of two isoforms.

Protein B23 is an abundant nucleolar phosphoprotein and putative ribosome assembly factor. Two forms of the protein, B23.1 and B23.2, contain 292 and 257 amino acids, respectively, and differ only in their C-terminal sequences. The two B23 isoforms have been produced in Escherichia coli using the pKK223-3 expression vector and purified to near homogeneity. The purification utilized ammonium sulfate fractionation followed by chromatography on DEAE-cellulose, heparin-Sepharose and Bio-Rad Q. By combined gel filtration and sedimentation analyses, both B23.1 and B23.2 formed multimers of Mr 210 to 255 kDa (apparent hexamers), suggesting that the differences in C-terminal ends of of the isoforms do not affect oligomerization. The oligomerization was not dependent on disulfide bond formation. The circular dichroism spectra of recombinant proteins B23.1 and B23.2 were similar suggesting that the carboxyl-terminal difference in the two proteins does not markedly influence overall secondary structure. Using routines for fitting the CD spectra to those of basis vectors the recombinant B23 isoforms appeared to be composed predominantly of beta-sheet and beta-turn secondary structures. Protein B23 from HeLa cell nuclei was recently shown to have a high affinity for the HIV-1 Rev protein. Using sucrose density gradient centrifugation it was shown that both recombinant proteins B23.1 and B23.2, as well as B23.1 isolated from Novikoff hepatoma nucleoli, were capable of binding the Rev protein.

Cell Nucleus↗