SEARCH · Search PubMed

Results for “Dimerization”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,549 records · Page 86Linked to original sources

PubMed1991

Double mixing stopped-flow method for the study of equilibria and kinetics of dimer-tetramer association of hemoglobins: studies on Hb Carp, Hb A, and Hb Rothschild.

A double mixing stopped-flow method is described for studying the dimer-tetramer equilibria of oxyhemoglobins and the kinetics of association of unliganded dimers. The three hemoglobins studied were: Hb Carp, Hb A, and Hb Rothschild (Trp beta 37 (C3)----Arg). The new method reproduces the data obtained for oxyHb A by other established methods. In agreement with previous studies, the new method indicates little, if any, dissociation of oxyHb carp into dimers even in 2 M urea solutions (0.1 M Bis-Tris pH 7.0). OxyHb Rothschild, on the other hand, is extensively dissociated into dimers (K(Hb4L4 in equilibrium with 2Hb2) = 37.3 x 10(-6) M) and the rate constant for the association of deoxy dimers of Hb Rothschild is about one-tenth of the value for Hb A indicating that the deoxy tetramer of Hb Rothschild is at least 10 times more dissociated into dimers than deoxyHb A.

Animals↗

PubMed1985

Functional characterization of the mitochondrial cytochrome b-c1 complex: steady-state kinetics of the monomeric and dimeric forms.

The QH2:cytochrome c oxidoreductase activity of the isolated bovine heart cytochrome b-c1 complex resolved into monomeric and dimeric form was titrated with three different inhibitors of electron transfer, antimycin, myxothiazol, and 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT). In all cases one inhibitor molecule per cytochrome c1 was found necessary to block completely the activity of both molecular forms of the enzyme. The antimycin-sensitive cytochrome c reduction catalyzed by the b-c1 complex was also studied as a function of increasing concentrations of either cytochrome c or quinol. Double-reciprocal plots of the activity of the monomeric enzyme were found linear either when the concentration of cytochrome c or of quinol derivatives, 2,3-dimetoxy-5-methyl-6-decyl-1,4-benzoquinol (DBH), and 2-methyl-3-undecyl-1,4-naphthoquinol (UNH), was changed. Cytochrome c reductase activity of the dimeric b-c1 complex also showed a linear Lineweaver-Burk plot as a function of cytochrome c concentrations. In contrast to the monomeric enzyme, however, dimers of the b-c1 complex express a clear nonlinear kinetic behavior toward quinol derivatives, with two apparent Km values differing approximately by one order of magnitude (about 3-4 and about 20-30 microM). At saturating quinol concentrations the activity of the dimeric enzyme becomes two to three times higher than that of monomers. The nonlinear kinetic plots were found to be the same at different temperatures and different cytochrome c concentrations. The data suggest that although the monomer of the b-c1 complex appears to be the functional unit of the enzyme, the dimer is more active. A regulatory role of the dimerization process resulting in an increase of the electrons flux through the enzyme is postulated.

Animals↗

PubMed1989

Dimer-tetramer equilibrium of glutathione reductase from the cyanobacterium Spirulina maxima.

Glutathione reductase [NAD(P)H:GSSG oxidoreductase; EC 1.6.4.2] from cyanobacterium Spirulina maxima exists as an equilibrium system between a dimer (S20,W = 5.96) and a tetramer (S20,W = 8.49) which has a very slow interconversion rate at neutral pH. Our results showed that the apparent dissociation constant (kd) was 4.61 X 10(-7) M. The proportion of both forms at pH 7.0 did not alter at either 4 or 25 degrees C. However, electrophoretic analysis at various pH values showed that at 25 degrees C a gradual transition takes place between oligomers with an apparent pKa of 7.55. When dimers aggregate to form tetramers, the reaction involves the uptake of eight protons (K = 1.58 X 10(-64) M9). At pH 7.7, the equilibrium shifts completely from dimers-tetramers to dimers when temperature is increased, which would suggest that the dissociation is an endothermic process. Thermodynamic parameters obtained from the temperature study show that the dissociation of glutathione reductase is characterized by positive entropy and enthalpy changes. Neither NADPH nor GSSG have any effect on the dimer-tetramer equilibrium. Measurements of reductase activity indicate that the tetramer is almost certainly active, whereas the dimer is either less active or inactive.

Cyanobacteria↗

PubMed1981

Lactose-H+(-OH) transport system of Escherichia coli. Multistate gated pore model based on half-sites stoichiometry for high-affinity substrate binding in a symmetrical dimer.

A model is proposed for the D-galactoside-H+(-OH) transporter of Escherichia coli that accounts for essentially all the experimental observations established for this system to date. In this model, the functional unit is postulated to be a dimer (consisting of two copies of lac Y-specified polypeptide) which spans the membrane with a 2-fold symmetry axis in the membrane plane (Lancaster, J.R. (1978) J. Theor. Biol. 75, 35-50). The functional dimer is assumed to possess a single pore flanked by an inner gate (gi) and an outer gate (go) and encompassing two oppositely oriented galactoside binding sites, designated m and mu. When go is open and gi is closed under non-energized conditions, binding site m adopts a configuration defined as State A (i.e., moA) exhibiting high affinity toward Class Ga galactosides (thiodigalactoside, melibiose, alpha-p-nitrophenygalactoside) but low affinity for Class Gb galactosides (lactose, beta-o-nitrophenylgalactoside, beta-isopropylthiogalactoside), whereas binding site mu adopts State B (i.e., muoB) displaying relatively high affinity toward Class Gb galactosides but comparatively low affinity for Class Ga galactosides; further, each moA : muoB dimer contains one thiol group whose reaction with N-ethylmaleimide inactivates the transporter unless blocked by galactoside binding at site moA, while the second homologous thiol of the dimer is unreactive toward thiol reagents. Translocation of the moA : muoB dimer involves closing of go followed by opening of gi, and causes the two thiols (as well as sites m and mu) to interchange roles in a symmetrical fashion: moA : muoB in equilibrium miB : muiA. In the presence of a substantial (negative) transmembrane delta potential of muH+, the m : mu dimer is postulated to undergo an electrogenic protein conformation change to a second form, *(m : mu), in which both sites m and mu possess low affinity toward internal Class Gb substrates; galactoside transport in both m : mu and *(m : mu) is assumed to be coupled to H+-symport (-OH-antiport) with a stoichiometry of approximately 1 : 1. Finally, five characteristic predictions of the half-sites model are outlined for further tests of its validity.

Cell Membrane↗

PubMed1977

Dimeric ("big") human placental lactogen. Immunological and biological activity.

Dimeric ("big") human placental lactogen has been isolated in near homogeneous form from placental tissue. It consists of a disulfide-linked (stable) form and a noncovalently associated (unstable) form of the native hormone. The two forms were separated by exposure to denaturing conditions and resolution by gel exclusion chromatography. Both forms retained immunological activity, ability to bind mammary membranes, and ability to induce mammary N-acetyllactosamine synthetase in vitro. On a molar basis, stable dimeric placental lactogen was more active than placental lactogen in the radioimmunoassay indicating that the immunological determinants on both monomeric units could bind to antibody. On a molar basis, stable dimeric placental lactogen was equally active with monomeric placental lactogen in competing for mammary gland membrane binding sites, indicating that only one active site in the molecule could interact with the membrane at a time. Stable dimeric placental lactogen was also active in an in vitro bioassay using the induction of N-acetyllactosamine synthetase. It is concluded that dimer formation does not alter the biologically active portion of the placental lactogen molecule. Since the carboxyl-terminal region (residues 182-191) is involved in the interchain disulfide bonds of dimeric placental lactogen, this portion of the molecule is probably not necessary for its biological activity.

Animals↗

PubMed1980

Micrococcus radiodurans surface exonuclease. Dimer to monomer conversion by ionizing radiation-generated aqueous free radicals.

Micrococcus radiodurans possesses an exonuclease firmly bound to a middle cell wall membrane layer. Aqueous OH. radicals generated chemically or by ionizing radiation cause the immediate release of this enzyme into the surrounding medium. The enzyme is located in a hydrophobic site and can also be released by aqueous n-butanol. When extracted by this solvent it is a non-covalently linker dimer and has a molecular weight of 260 000 as determined by gel filtration. When released by radiation generated OH. radicals, the enzyme initially appears in solution as the dimer but is rapidly split by further aqueous radical attack into two 130 000 molecular weight subunits. Hydroxyl radicals are most effective but reducing radicals are also able to monomerize the enzyme. Only the released dimer enzyme is subject to free radical monomerization. Bound dimer enzyme is not split prior to release. No detectable loss of activity or change in catalytic properties accompanies the free radical cleavage of the enzyme. Both subunits of the dimer enzyme possess a tightly bound metal ion (probably Ca2+) required for activity. The monomer but not the dimer enzyme will bind to an anion exchanger. The monomer is susceptible to loss of its metal ion, and consequent inactivation, when exposed to the exchanger in the absence of Ca2+. Besides providing information on some of the immediate non-lethal effects of ionizing radiation, the behavior of this enzyme system demonstrates a potential cellular mechanism by which internally or externally generated free radicals could be utilized by the cell to control various enzymic reactions.

Butanols↗

PubMed1987

Interaction of dimers of inactive enkephalin fragments with mu opiate receptors.

Dimeric analogues of the inactive enkephalin fragment Tyr-D-Ala-Gly were synthesized by cross-linking with alkanediamine at the C-terminus. Biological evaluation of these dimers (H-Tyr-D-Ala-Gly-NH)2.(-CH2-)n (DTREn), where n = 0-6, revealed that the fragment inactive for mu receptors was activated by its dimerization, with the maximum activation found with DTRE2, and that the dimer was highly mu-selective. So-called "handicapped" dimers, which lack one of the essential groupings required for enkephalin activity, were found to be far less active, indicating that the dimer interacts bivalently with mu receptors. It seems, therefore, that mu opiate receptors contain at least two equivalent binding sites which are extremely close to each other.

Animals↗

PubMed1989

Dimerization of hepatitis B viral X protein synthesized in a cell-free system.

Hepatitis B viral X protein (HBx), a 17-kDa polypeptide, has been demonstrated as a trans-acting factor. In this study, we report that the HBx was able to form a dimer, a feature very similar to many well known trans-acting factors. In vitro synthesized HBx, after immunoprecipitation and analysis by SDS-PAGE, appeared as one prominent 17-kDa band (monomer) and a faint 34-kDa band (dimer). The amount of dimer increased if the sample of immunoprecipitated HBx was not treated with 2-mecaptoethanol, indicating the dimer was held together by the disulfide linkage. Dimerization of a truncated HBx established that the four cysteine residues close to the N-terminus are sufficient for the dimerization process.

Cell-Free System↗

PubMed1989

Quantitative dissociation of glucose transport stimulation and insulin receptor tyrosine kinase activation in isolated adipocytes with a covalent insulin dimer (B29,B29'-suberoyl-insulin).

The covalent insulin dimer B29,B29'-suberoyl-insulin was investigated for its effects on insulin receptor binding, insulin receptor tyrosine kinase activity and glucose transport in isolated adipose cells. The dimer stimulated glucose transport (initial 3-O-methylglucose uptake rate) to the same extent as insulin did (basal rate, 35 +/- 3 pmol/sec/microliter lipid; insulin, 380 +/- 27; B29,B29'-suberoyl-insulin, 369 +/- 24, means +/- S.E.), although at higher concentrations (EC50 1.94 +/- 0.64 nM versus 0.1 +/- 0.02 with insulin). In contrast, the dimer only partially (23%) mimicked insulin's effect on phosphate incorporation into insulin receptors immunoprecipitated after equilibration of cells with [32P]phosphate. Similarly, insulin receptor tyrosine kinase as assessed by receptor autophosphorylation and phosphorylation of the substrate poly-(Glu/Tyr) was not fully activated by treatment of cells with the insulin dimer (31 and 42% of the effect of insulin, respectively) in concentrations which maximally activate glucose transport and give rise to full insulin receptor occupancy (5 X 10(-7) M). Further, the dimer activated the receptor tyrosine kinase in solubilized purified insulin receptor preparations from adipose cells to only 25% of the effect of insulin (EC50 32.0 +/- 16 versus 1.9 +/- 1.0 nM with insulin) in spite of full receptor occupancy. Binding of the dimer to insulin receptors followed single site binding kinetics, indicating that the derivative is unable to induce negative cooperativity of the insulin receptor. It is concluded that a partial phosphorylation of insulin receptors and a submaximal tyrosine kinase activation are sufficient for full stimulation of glucose transport in the adipocyte. Further, it is suggested that negative cooperativity of the insulin receptor and activation of its tyrosine kinase require a similar conformational change of the receptor protein.

Adipose Tissue↗

PubMed1989

DNA binding, cytotoxicity and inhibitory effect on RNA synthesis of two new 1-nitro-9-aminoacridine dimers.

Two 1-nitro-9-aminoacridine dimers were prepared: one bearing a spermine flexible linking chain, compound 4, the other a rigid dipiperidine-type linker, compound 7. Both dimers elicited a higher affinity constant for DNA than the parent monomeric drug nitracrine 2. This affinity was several orders lower than what was found for other dimeric compounds having the same linkers and no nitro group on the acridine ring (3, 5, 6 and 8). Bisintercalation was evidenced for compound 4 by viscosimetric measurements. In the absence of dithiothreitol, an inhibitory effect of RNA synthesis in vitro was observed for all the tested compounds except 2 and 7. In the presence of dithiothreitol, 4 and 7 formed irreversible complexes with DNA of decreased template properties. The level of the dimers binding was lower than that of the parent compound 2. Cross-links were detected by means of hydroxylapatite chromatography in a complex of the dimer bearing a flexible linking chain, compound 4 with DNA, while the compound 7-DNA complex eluted in the single-stranded DNA region. The extent of cytotoxicity of the two 1-nitro-9-aminoacridine dimers against L1210 cultured cells was different.

Aminoacridines↗

PubMed1992

Structure refinement of the chromomycin dimer-DNA oligomer complex in solution.

We have refined the initial docking model of the Mg(II)-co-ordinated chromomycin-d(A2G2C2T2) complex (2 drug equivalents per duplex) by a complete relaxation matrix analysis simulation of the two-dimensional nuclear Overhauser effect (NOESY) spectrum of the complex in 2H2O solution. This relaxation matrix refined structure of the complex exhibits the following characteristics. (1) We observe an unwound and elongated duplex that exhibits characteristics distinct from the A and B-DNA family of helices at the central (G-G-C-C).(G-G-C-C) chromomycin dimer binding and flanking sites. On the other hand sugar puckers, glycosidic torsion angles, displacement of the base-pairs from the helix axis and the minor groove width for this central tetranucleotide segment all fall within the A-family of helical parameters. (2) The chromomycin monomers are aligned in a head-to-tail orientation in the Mg(II)-co-ordinated dimer in the complex. The chromophores are aligned with a slight tilt relative to each other and make an angle of 75 degrees between their planes. The C-D-E trisaccharide segments from individual monomers adopt an extended conformation that projects in opposite directions in the dimer. The divalent metal cation is co-ordinated to the O(1) carbonyl and O(9) enolate atoms of the chromophores and aligns them such that the O(9)-Mg-O(9) angle is 170 degrees while all other O-Mg-O angles are in the 95(+/- 15)degrees range. (3) The sequence specificity of the chromomycin dimer for the widened and shallower (G3-G4-C5-C6).(G3-G4-C5-C6) minor groove binding site is associated with intermolecular hydrogen bonds formed between the OH group at C(8) of the chromophore and the minor groove NH2 group at position 2 and N(3) groups of G4 and between the O(1) oxygen of the E-sugar and the minor groove NH2 group at position 2 of G3 in the complex. (4) Additional intermolecular interactions are primarily van der Waals contacts between anomeric and adjacent CH2 protons on each sugar in the C-D-E trisaccharide segments of the chromomycin dimer and the minor groove surface of the DNA. These results provide insights into the induced conformational transitions required to generate a complementary match between the drug dimer and its DNA binding site on complex formation.

Base Sequence↗

PubMed1984

Murine retrovirus Pr65gag forms a 130K dimer in the absence of disulfide reducing agents.

Gazdar-murine sarcoma virus (Gz-MSV) particles, obtained from tissue culture fluids of chronically infected HTG-2 hamster cells are immature in morphology and contain uncleaved Pr65gag as the predominant protein (greater than 95% Coomassie blue stain) (A. Pinter and E. deHarven, 1979, Virology 99, 103-110; Y. Yoshinaka and R. B. Luftig, 1982, Virology 118, 380-388). When Gz-MSV particles are disrupted in 1% sodium dodecyl sulfate (SDS) and then analyzed by SDS-polyacrylamide gel electrophoresis (PAGE) in the absence of reducing agents, such as beta-mercaptoethanol (beta-MSH) almost half of the Pr65gag Coomassie blue-stained band is detected as a band at a Mr of 130K. Electrophoretic blotting studies with monospecific antisera against MuLV p30, p15, p12, and p10 showed that the 130K band cross-reacted with all four antigens suggesting that it was a dimer of Pr65gag. Two-dimensional (2D) SDS-PAGE where the first dimension was run under nonreducing conditions and the second with beta-MSH, supported the contention that the 130K band was a dimeric complex of Pr65gag. One also saw minor amounts of a 260K and higher polymeric forms of Pr65gag on the SDS gels, suggesting that polymeric forms may exist as well. When 32P-labeled Gz-MSV particles obtained by in vivo labeling of infected HTG-2 cells with [32P]PPi were electrophoresed on SDS-PAGE, only 10% of the 32P label was detected at the 130K position. In contrast, 30% of the Coomassie blue-stained Pr65gag material was found at 130K on the 2D gels. This suggests that unphosphorylated Pr65gag is more likely to participate in dimer formation than phosphorylated Pr65gag. Pr65gag of Moloney murine leukemia virus (M-MuLV), which is present as a minor (5% of stain) protein band on SDS-PAGE also showed 130K dimers. Further, in beta-MSH-deficient SDS preparations of Gz-MSV, electrophoresed after trypsin treatment, a 32K band that stained with p15, but not p10, p12, nor p30, antisera was observed. If beta-MSH was added, this band was no longer present. Thus Pr65gag dimerization in immature MuLV particles appears to at least involve the p15 region of the polyprotein. Since p15 is an extremely hydrophobic protein, formation of Pr65gag dimers may occur when virion precursor proteins are brought to the cell membrane during virus assembly.

Animals↗

PubMed1991

Which factors affect high D-dimer levels in the elderly?

To study the age-related changes in plasma D-dimer levels and the effect of atherosclerotic disease and long-term immobilization on haemostasis the elderly, we measured plasma D-dimer levels in 148 subjects aged from 60 to 94 years using an ELISA. We also measured plasma fibrinogen, serum uric acid, total cholesterol, triglycerides, HDL cholesterol, beta-lipoprotein fractions, and apolipoproteins (A-I, A-II, B, E). Plasma D-dimer levels (326 +/- 148 ng/ml) were significantly higher in the healthy elderly subjects than in younger controls (180 +/- 58 ng/ml, p less than 0.01) and increased further with age (r = 0.344, p less than 0.01). D-dimer levels were significantly higher in elderly women than in elderly men (p less than 0.05). The D-dimer level correlated significantly with both the fibrinogen antigen level (r = 0.286, p less than 0.001) and the clotting activity (r = 0.275, p less than 0.01), and also correlated with apolipoprotein E levels. There were no correlations with the other parameters assessed. The D-dimer levels were significantly higher in the elderly subjects with atherosclerotic disease (516 +/- 285 ng/ml) than in healthy elderly subjects (p less than 0.001). Moreover, the levels were even higher in elderly subjects with long-term immobilization (866 +/- 408 ng/ml) than in subjects with atherosclerosis, even after age, sex and underlying diseases were taken into consideration. These results indicate that coagulation and fibrinolysis activity are increased in the elderly, especially those with atherosclerotic disease and that moreover long-term immobilization further accelerates their haemostatic hyperactivity.

Aged↗

PubMed1988

Dimers of human immunoglobulin G1 provide an insufficient signal for their degradation by human monocytes.

In order to better define the processing of small soluble immune complexes by normal human monocytes, we have characterized the binding and degradation of human IgG1 monomers and covalently crosslinked dimers and heavier oligomers (composed predominantly of trimers, tetramers, and pentamers) by these cells. Whereas 15,000 molecules of monomeric IgG1 bound, about 110,000 and 65,000 IgG1 protomers of the oligomers and dimers, respectively, bound to the monocytes. Dimers bound dimerically to the cells as demonstrated by their enhanced rate of dissociation in the presence of excess heat-aggregated gamma-globulin. Despite occupying two Fc receptors, the intracellular fate of dimers was essentially that of the monomers; only 5-10% of the bound protomers were degraded. In contrast, approximately 40,000 IgG protomers of the heavy oligomers (30% of total bound) were degraded over a 5-hr incubation period. Since binding of a heavier complex, is required for degradation by the monocyte, dimeric immune complexes can generally escape the normal clearance mechanisms of the host.

Antigen-Antibody Complex↗

PubMed1990

Three-dimensional structure of a hybrid light chain dimer: protein engineering of a binding cavity.

An attempt was made to engineer a binding site and check its structure by X-ray analysis. Two human light chains (Mcg and Weir), with "variable" domain sequences differing in 36 positions, were hybridized into a heterologous dimer and crystallized in ammonium sulfate by the same procedure used for the trigonal form of the Mcg dimer. The three-dimensional structure of the hybrid was determined at 3.5-A resolution by difference Fourier analysis, interactive model building with computer graphics and crystallographic refinement. In the heterologous dimer, the Weir protein behaved as the structural analog of the heavy chain in an antigen binding fragment, while the Mcg protein assumed the role of the light chain component. The hybrid and the Mcg dimer were closely similar in overall structure, an observation probably correlated with the deliberate cleavage of the intrachain disulfide bond in the variable domain of the Weir protein during the hybridization procedure. Examination of the crystal structure of the hybrid suggested that the cleavage resulted in the relaxation of restraints which might otherwise have interfered with the formation of an Mcg-like dimer. There were six substitutions among the residues lining the binding cavities of the hybrid and Mcg dimer. These substitutions significantly affected the sizes, shapes and binding properties of the two cavities.

Amino Acid Sequence↗

PubMed1995

Covalently-bound human C4b dimers consisting of C4B isotype show higher hemolytic activity than those of C4A in the C3-bypass complement pathway.

The ability to form a covalent dimer of human C4b was investigated with purified isotypes C4A and C4B, and antibody-sensitized liposomes supplemented with C1. In this system, no C4A or C4B formed a complex with the antibody or C1. Whereas both C4A and C4B isotypes formed dimers to a similar extent, C4B formed an ester-linked dimer and C4A an amide-linked dimer. Both of these dimers served as a subunit for the C3-bypass pathway C5 convertase, since liposomes bearing Ab, C1 and a dimer of C4A or C4B, allowed the formation of C5 convertase by the addition of C2. The degree of complement-mediated liposome lysis however, was observed to be 2-3 times higher in the C4B-bearing particles than in those bearing C4A. These results indicate that the second C4b-binding site on the first C4b is different between C4A and C4B, and that in the C3-bypass pathway, C4B has a higher degree of hemolytic activity than C4A, as in the conventional classical complement pathway.

Biopolymers↗

PubMed1983

Subunit interactions in the dimeric and tetrameric hemoglobins from the mollusc Scapharca inaequivalvis.

The dissociation behaviour of oxygenated Scapharea inaequivalvis HbII, the tetrameric hemoglobin component contained in the erythrocytes of this bivalve mollusc, has been compared with that of oxygenated human hemoglobin, HbA. At neutral pH the molluscan protein dissociates reversibly into dimers as does HbA, although dissociation is less marked; moreover the dimer-tetramer association constant is not sensitive to the presence of inorganic phosphates and high salt concentrations. HbII dimers hybridize with HbA dimers in solution, pointing to an overall similarity of the dimer interfaces in these hemoglobins from distantly related species. The gel filtration behaviour of the dimeric hemoglobin component of the erythrocytes. HbI, indicates that at neutral pH the protein has very little tendency to dissociate into monomers even at micromolar concentrations. Hb I was found to contain small amounts (2-4%) of bound carbohydrates.

Animals↗

PubMed1984

The structure of the histone dimer H2A-H2B studied by spectroscopy.

The spatial organization of the histone dimer (H2A-H2B) in 0.1-1.0 M NaCl is characterized by the inclusion of 38% of the residues in alpha-helical segments, an average fluorescence quantum yield of 0.085 +/- 0.003, a red shift of absorption (lambda max = 278 +/- 0.5 nm) and fluorescent spectra (lambda max = 304.4 +/- 0.3 nm) as compared to the respective spectra of free tyrosine. The changing of position lambda max of tyrosine fluorescence of histones during denaturation has been shown. The dimer (H2A-H2B) exhibited a conformational change in a transition centred at about 0.5 M NaCl. The dimer denaturation takes place at higher urea concentrations as the ionic strength of the medium increases. The quenching of tyrosine fluorescence of the histone dimer (H2A-H2B) was performed using the ions I-, Cs+ and acrylamide. It has been shown that, at a concentration of NaCl over 0.5 M, dimer compactization takes place, as well as the screening of some part of tyrosyls for te against the quenching effect of Cs+. Our experiments made it possible to identify three zones in the composition of the histone dimer (H2A-H2B) and determine the number (ni) and fluorescence quantum yields (qi) of tyrosyls included in the following specific zones: zone I, n1 = 2, q1 = 0.136; zone II, n2 = 3; q2 = 0.08; zone III, n3 = 3; q3 = 0.055.

Animals↗