A kinetic model for magnetostriction of a ferrogel with physical networking.

Kinetics of magnetostriction of ferrogel with physical networking based on natural polysaccharide guar gum with embedded strontium hexaferrite magnetic particles were studied in the uniform magnetic field 420 mT. An ellipsoidal sample was elongated by 37% along the applied field and contracted by 15% in the transverse direction, while its volume was kept constant. The characteristic time of magnetostriction was 440 s. Dynamic mechanical analysis in an oscillatory mode showed that the deformation of ferrogel is mostly elastic rather than viscous. Its storage modulus was almost constant in a frequency range of 0.1-100 Hz and by at least an order of magnitude larger than the loss modulus. Meanwhile, a developed theoretical model based on the elasto-viscous behaviour of the ferrogel failed to estimate correctly the experimental value of its magnetostriction. Calculated values of the elongation of ferrogel in the field were several orders of magnitude lower than those observed in the experiment for the ferrogel with physical networking. Consistency between the experiment and the theory was achieved using the alternative consideration based on the deformation of a liquid droplet of ferrofluid. The applicability of such an approach was discussed concerning structural relaxation properties of the ferrogel with physical networking. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

[Functional asymmetry of electric processes in the rabbit brain cortex at formation of the hunger dominant].

The motivational condition of hunger and formation of the hunger dominant after daily food deprivation was studied in the conditions of chronic experiments on rabbits. It was shown, that the hunger condition was accompanied by left sided interhemispher asymmetry on indicators of spectral capacity of EEG frontal and right-hand asymmetry sensorimotor areas of the cortex. A hunger dominant was accompanied by falling of spectral capacity of EEG of areas of both hemispheres. The condition of hunger and a hunger dominant were characterized by right-hand asymmetry on average level of EEG coherence of frontal and sensorimotor areas. At transition of a condition of hunger in a hunger dominant there was an average level of EEG coherence decrease in areas of the right hemisphere. Electric processes of the cortex of the brain at a motivational condition of hunger and a hunger dominant were different.

[Experimental evidence for simultaneous existence of two dominantas in the central nervous system].

For the first time a possibility of simultaneous existence of two dominants was demonstrated: the polarization in the cortical representation of the forelimb and the dominanta of hunger. The two foci of stable excitation were created at the subthreshold level. A sound stimulus simultaneously produced a movement of the forelimb and a gulp. Manifestation of the two dominantas could be observed over the course of the experiment (about 1 h).

Dynamics of changes in electrical activity in the rabbit cerebral cortex during sequential sessions of "animal hypnosis".

The dynamics of changes in individual electrical activity rhythms in the premotor, sensorimotor, and temporal-parietal areas of the cortex in both hemispheres were studied in chronic experiments in rabbits during sequential sessions of "animal hypnosis." These experiments showed that during the first session of "animal hypnosis," significant changes in electrical activity occurred only in the premotor area of the cortex of the right hemisphere, where there were increases in spectral power in the delta-1 and delta-2 ranges and decreases in spectral power in other ranges of electrical activity. Subsequent sessions of "animal hypnosis" formed increasing changes in electrical activity, which were particularly marked in cortical areas in the right hemisphere. Significant changes in spectral power in the delta and theta ranges of electrical activity in cortical areas did not arise at the beginning of the hypnotic state, but after 4-6 min. During the third session of "animal hypnosis," the course of electrical activity in the alpha and beta rhythms in the premotor and sensorimotor areas of the cortex became wave-like in nature.

[Interaction of stationary excitation foci in the rabbit brain].

Influence of "animal hypnosis" on the motor polarization dominanta created by direct anodic current applied on the left sensorimotor cortex of the rabbit ("left" dominanta) was studied in chronic experiments. Animal behavior and electrophysiological characteristics were recorded. It was impossible to elicit the "animal hypnosis" during the optimum of the "left" dominanta. The state of "animal hypnosis" could be easily elicited against the background of the latent focus of the "left" dominanta on the next day after its formation. The "animal hypnosis" restored the "left" dominanta after its extinction. It was accompanied by formation of a new pattern of the cortical EEG coherence in the delta range, which was different from the patterns characteristic of each kind of dominanta. After the "animal hypnosis" session, the formation of the "left" dominanta produced two kinds of nonstable foci. During testing, the "left" dominanta reached its optimum and then inhibited the tonic activity of the right forelimb characteristic of the "animal hypnosis". The interaction of the "animal hypnosis" and the dominant foci in the left and right sensorimotor cortex were different.

[The dynamics of modification of electrical activity of the rabbit brain during consistent "animal hypnosis" series].

The dynamics of modification of individual rhythms of electrical activity in both hemispheres was studied under condition of chronic experiments in rabbits during "animal hypnosis" sessions. It was shown that, after the first "animal hypnosis" session, significant changes in the spectral power of electrical activity appeared only in the right premotor cortical area. They consisted in an increase in the spectral power of the delta1 and delta2 rhythms and a decrease in the spectral power of the other rhythms. During the next "animal hypnosis" sessions, changes in the electrical activity became stronger, especially in the right hemisphere. Significant changes in the spectral power of the delta and theta rhythms appeared not at the beginning of the "animal hypnosis" session but 4-6 min later. During the third "animal hypnosis" session, the power of the alpha and beta rhythms in the premotor and sensorimotor cortical areas of both hemispheres varied in an undulatory way.

[Motor polarization dominance and "animal hypnosis"]. / Dvigatel'naia poliarizatsionnaia dominanta i "zhivotnyi gipnoz".

Two kinds of dominanta were simultaneously formed under conditions of chronic experiments in rabbits. The motor polarization dominanta was formed under exposure of the right sensorimotor cortex of an animal to direct anodic current, and the state of "animal hypnosis" (the second dominanta) was induced. Animal behavior and electrophysiological characteristics were recorded. It was shown that the "animal hypnosis" induced at the optimum of the right motor polarization dominanta inhibited the motor reaction of the "dominant" extremity to testing stimuli. After the "animal hypnosis session, exposure of the right sensorimotor cortex to anodic current produced the latent excitation focus, which did not reach the level of summation. Two days later, exposure to testing stimuli developed the latent foci at first in the right cortex and then in subcortical structures. In the course of recovery of the motor polarization dominanta and its further change for the state characteristic of the "animal hypnosis", the patterns of cortical EEG coherence in the delta range typical of each kind of dominanta alternated in parallel with the time course of state changes.

[Intercentral reticulo-cortical relations of brain electrical activity during "animal hypnosis" in rabbits]. / Mezhtsentral'nye retikulo-kortikal'nye otnosheniia électricheskoi aktivnosti vo vremia sostoianiia 'zhivotnogo gipnoza' u krolikov.

The electrical activity of the right and left sensorimotor and premotor cortical areas and right and left medulary reticular formation was recorded during "animal hypnosis" in rabbits. In this state, the spectral power of potentials (predominantly, in the delta-range) recorded from the left reticular formation was higher than that recorded from the right side. The value of the function of coherence between the right and left reticular recordings was decreased to 0.1-0.2 in the whole frequency range. The tight-side intrahemispheric coherence between the activities recorded from the sensorimotor cortex and reticular formation was higher than respective left-side values, whereas the coherent relations between the activities recorded from the reticular formation and premotor cortex were not changed (as compared to nonhypnotic state).

Multiple activation loop conformations and their regulatory properties in the insulin receptor's kinase domain.

Low catalytic efficiency of protein kinases often results from intrasteric inhibition caused by the activation loop blocking the active site. In the insulin receptor's kinase domain, Asp-1161 and Tyr-1162 in the peptide substrate-like sequence of the unphosphorylated activation loop can interact with four invariant residues in the active site: Lys-1085, Asp-1132, Arg-1136, and Gln-1208. Contributions of these six residues to intrasteric inhibition were tested by mutagenesis, and the unphosphorylated kinase domains were characterized. The mutations Q1208S, K1085N, and Y1162F each relieved intrasteric inhibition, increasing catalytic efficiency but without changing the rate-limiting step of the reaction. The mutants R1136Q and D1132N were virtually inactive. Steric accessibility of the active site was ranked by relative changes in iodide quenching of intrinsic fluorescence, and A-loop conformation was ranked by limited tryptic cleavage. Together these ranked the openness of the active site cleft as R1136Q approximately D1132N > or = D1161A > Y1162F approximately K1085N > Q1208S > or = wild-type. These findings demonstrate the importance of specific invariant residues for intrasteric inhibition and show that diverse activation loop conformations can produce similar steady-state kinetic properties. This suggests a broader range of regulatory properties for the activation loop than expected from a simple off-versus-on switch for kinase activation.

Intrasteric inhibition of ATP binding is not required to prevent unregulated autophosphorylation or signaling by the insulin receptor.

Receptor tyrosine kinases may use intrasteric inhibition to suppress autophosphorylation prior to growth factor stimulation. To test this hypothesis we made an Asp1161Ala mutant in the activation loop that relieved intrasteric inhibition of the unphosphorylated insulin receptor (IR) and its recombinant cytoplasmic kinase domain (IRKD) without affecting the activated state. Solution studies with the unphosphorylated mutant IRKD demonstrated conformational changes and greater catalytic efficiency from a 10-fold increase in k(cat) and a 15-fold-lower K(m ATP) although K(m peptide) was unchanged. Kinetic parameters of the autophosphorylated mutant and wild-type kinase domains were virtually identical. The Asp1161Ala mutation increased the rate of in vitro autophosphorylation of the IRKD or IR at low ATP concentrations and in the absence of insulin. However, saturation with ATP (for the IRKD) or the presence of insulin (for the IR) yielded equivalent rates of autophosphorylation for mutant versus wild-type kinases. Despite a biochemically more active kinase domain, the mutant IR expressed in C2C12 myoblasts was not constitutively autophosphorylated. However, it displayed a 2.5-fold-lower 50% effective concentration for insulin stimulation of autophosphorylation and was dephosphorylated more slowly following withdrawal of insulin than wild-type IR. In tests of the regulation of the unphosphorylated basal state, these results demonstrate that neither intrasteric inhibition against ATP binding nor suppression of kinase activity is required to prevent premature autophosphorylation of the IR. Finally, the lower rate of dephosphorylation suggests invariant residues of the activation loop such as Asp1161 may function at multiple junctures in cellular regulation of receptor tyrosine kinases.

[Interaction between two excitation foci in the central nervous system capable for summation]. / Vzaimodeistvie dvukh ochagov vozbuzhdeniia v tsentral'noi nervnoi sisteme, obladaiushchikh svoistvom summatsii.

The interaction between two dominant foci was carried out on different models of dominant. It was shown that the following pairs: latent motor and blinking excitation foci; hunger and hypnotic dominants, decaying polarization dominant (related with functioning of the left-hemisphere) and hypnotic dominant can function simultaneously. After repeated formation of a new dominant focus against the background of the existing stable dominant created earlier, a replacement of dominants takes place. This process passes through the stage of formation of the latent dominant not yet apparent at the behavioral level but with the electrical activity typical for the dominant focus. Actually, two dominants exist at this stage: the previous active and latent foci. The latter determines further behavior of the animal.

[Interactions between electrical activities of the sensomotor cortex and the hippocampus during 'animal hypnosis' in rabbits]. / Vzaimootnosheniia élektricheskoi aktivnosti sensomotornoi kory i gippokampa pri "zhivotnom gipnoze" u krolikov.

The electrical activity of the left and right sensorimotor cortex and left and right dorsal hippocampus (CA3 fields) was recorded during "animal hypnosis" in rabbits. The "animal hypnosis" produced asymmetry in the spectral power of the hippocampal electrical activity due to an increase in the power of delta 1, delta 2, and theta 1 components in the left-hippocampus and decrease in the spectral power in the same ranges in the right-hippocampus. Hemispheric asymmetry in the electrical activity during the "animal hypnosis" was also expressed in the indices of coherence between the sensorimotor cortex and hippocampus. EEG coherence between the left sensorimotor cortex and left hippocampus in the delta 1, theta 1, and theta 2 ranges was higher than that between the right-side structures.

The structure of cortical-subcortical relationships between electrical processes of the brain during a motor polarization dominant.

Coherence analysis of electrical activity was applied to chronic experiments on rabbits and showed that the formation of a motor polarization dominant, created by the action of an anodic direct current applied to the sensorimotor cortex, evoked a general rearrangement of the structure of cortical-subcortical relationships between electrical processes not only in the "dominant," but also in the opposite half of the brain. Zones of primary excitation foci became isolated in the cortex of the "dominant" hemisphere, with a reduction in their coherent electrically active connections, in the delta range, with other areas of the cortex. In conditions of an optimal dominant, interstimulus intervals showed asymmetry in delta-range coherence in the electrical activity of the sensorimotor cortex and the ventrolateral nucleus of the thalamus and field CA3 of the hippocampus of the "dominant" and "non-dominant" halves of the brain, which was increased in response to sound stimuli. Asymmetry in the alpha and beta ranges of coherence spectra for the electrical activity of the areas studied, coinciding with the performance of a motor "dominant" response, was associated with the processes involved in organizing the movement.

Probing local environments of tryptophan residues in proteins: comparison of 19F nuclear magnetic resonance results with the intrinsic fluorescence of soluble human tissue factor.

19F nuclear magnetic resonance (19F NMR) of 5-fluorotryptophan (5F-Trp) and tryptophan (Trp) fluorescence both provide information about local environment and solvent exposure of Trp residues. To compare the information provided by these spectroscopies, the four Trp residues in recombinant soluble human tissue factor (sTF) were replaced with 5F-Trp. 19F NMR assignments for the 5F-Trp residues (14, 25, 45, and 158) were based on comparison of the wild-type protein spectrum with the spectra of three single Trp-to-Phe replacement mutants. Previously we showed from fluorescence and absorption difference spectra of mutant versus wild-type sTF that the side chains of Trpl4 and Trp25 are buried, whereas those of Trp45 and Trp158 are partially exposed to bulk solvent (Hasselbacher et al., Biophys J 1995;69:20-29). 19F NMR paramagnetic broadening and solvent-induced isotope-shift experiments show that position 5 of the indole ring of 5F-Trp158 is exposed, whereas that of 5F-Trp45 is essentially inaccessible. Although 5F-Trp incorporation had no discernable effect on the procoagulant cofactor activity of either the wild-type or mutant proteins, 19F NMR chemical shifts showed that the single-Trp mutations are accompanied by subtle changes in the local environments of 5F-Trp residues residing in the same structural domain.

[The structure of the cortical-subcortical relationships of the cerebral electrical processes during a motor polarization dominant]. / Struktura korkovo-podkorkovykh otnoshenii élektricheskikh protsessov mozga pri dvigatel'noi poliarizatsionnoi dominante.

Under conditions of rabbit chronic experiments, it was shown by means of the spectral-coherence analysis that the motor polarization dominant formed by the application of DC anode to the sensorimotor cortex produced a novel structure of the intercentral relations between electrical processes not only in the ipsi-, but in the contralateral brain hemisphere. A certain "isolation" of the primary focus was observed in the cortex of the "dominant" hemisphere, which was manifested in a decrease in its delta-range coherent relations with the other cortical areas. At the dominant optimum (in interstimulus intervals), an interhemispheric asymmetry in the EEG coherence spectra was observed in the delta band between the sensorimotor cortical areas, ventroposterolateral thalamic nuclei, and CA3 fields of the dorsal hippocampi. The asymmetry increased during the testing auditory stimulation. Development of the alpha- and beta-band interhemispheric asymmetry in the structures in question coincided with realization of the motor "dominant" reaction and was suggested to be associated with movement organization.

Antiphospholipid antibodies accelerate plasma coagulation by inhibiting annexin-V binding to phospholipids: a "lupus procoagulant" phenomenon.

The antiphospholipid syndrome is a thrombophilic condition marked by antibodies that recognize anionic phospholipid-protein cofactor complexes. We recently reported that exposure to IgG fractions from antiphospholipid patients reduces the level of annexin-V, a phospholipid-binding anticoagulant protein, on cultured trophoblasts and endothelial cells and accelerates coagulation of plasma exposed to these cells. Therefore, we asked whether antiphospholipid antibodies might directly reduce annexin-V binding to noncellular phospholipid substrates. Using ellipsometry, we found that antiphospholipid IgGs reduce the quantity of annexin-V bound to phospholipid bilayers; this reduction is dependent on the presence of beta2-glycoprotein I. Also, exposure to plasmas containing antiphospholipid antibodies reduces annexin-V binding to phosphatidyl serine-coated microtiter plates, frozen thawed washed platelets, activated partial thromboplastin time (aPTT) reagent and prothrombin time reagent and reduces the anticoagulant effect of the protein. These studies show that antiphospholipid antibodies interfere with the binding of annexin-V to anionic phospholipid and with its anticoagulant activity. This acceleration of coagulation, due to reduced binding of annexin V, stands in marked contrast to the "lupus anticoagulant effect" previously described in these patients. These results are the first direct demonstration of the displacement of annexin-V and the consequent acceleration of coagulation on noncellular phospholipid surfaces by antiphospholipid antibodies.

Linkage between operator binding and dimer to octamer self-assembly of bacteriophage lambda cI repressor.

Cooperative binding of the bacteriophage lambda cI repressor dimer to specific sites of the phage operators OR and OL controls the developmental state of the phage. Cooperativity has long been thought to be mediated by self-assembly of repressor dimers to form tetramers which can bind simultaneously to adjacent operators. More recently, we demonstrated that when free repressor dimers self-associate in solution, tetramer is an intermediate in a concerted assembly reaction leading to octamer as the predominant higher order species [Senear, D. F., et al. (1993) Biochemistry 32, 6179-6189]. Even as a minority component in the assembly reaction, tetramer can account for pairwise cooperativity. In a similar manner, were it able to bind all three operators simultaneously, octamer could account for three-way cooperativity. In fact, based solely on repressor self-assembly, the naive prediction is that the repressor-OR interactions should be substantially more cooperative than they are. Evidently, there are unfavorable contributions to cooperativity from processes other than repressor self-assembly. Here, we focus on coupling between repressor self-association and operator binding as one possible unfavorable contribution to cooperativity. Sedimentation equilibrium analysis was used to compare the dimer-octamer association reactions of a repressor dimer-OR1 complex and free repressor dimer. Fluorescence anisotropy was used to investigate OR1 binding to free dimers and dimers assembled as higher order species. The results of these experiments indicate a significant and salt-dependent unfavorable contribution generated by such coupling. Since the oligonucleotides used in these experiments are the size of single operator sites, this coupling is mediated by the protein, not by the DNA. This mechanism does not account for an additional, salt-independent, unfavorable contribution which we presume is transmitted via the DNA. Thus, unfavorable contributions generated by structural transitions in both macromolecules serve to moderate the effect of self-association alone. We speculate that this is a general feature of cooperative protein-DNA interactions.

Effect of stimulation of the medial geniculate body on the motor polarization dominant in rabbits.

Studies were carried out on the effects of stimulation of the medial geniculate body on the course and recovery of a cortical motor polarization dominant created in the sensorimotor cortex of the right hemisphere in rabbits. Stimulation of the medial geniculate body, on a background of an optimum dominant, elicited a movement response of the "dominant" limb. Spectral-coherent analysis of the electrical activity of the sensorimotor cortex and medial geniculate body showed that stimulation produced changes characteristic of the dominant state in the power spectra of the total activity of these structures of the right "dominant" half of the brain, as well as in the coherence spectra.

An aromatic stacking interaction between subunits helps mediate DNA sequence specificity: operator site discrimination by phage lambda cI repressor.

Sequence specific DNA binding by regulatory proteins provides the basis for regulation of initiation of transcription. A great deal of progress has been made toward understanding sequence specific recognition by individual protein subunits. An additional level of control that needs to be understood is that due to coupling between the subunits of oligomeric regulatory proteins. An example is the bacteriophage lambda cI repressor, a dimeric protein that regulates the lysogenic to lytic genetic switch of the phage. Two levels of specificity are critical to this regulation. First, like all transcriptional regulators, dimers distinguish operator from nonspecific DNA. Direct readout of the DNA sequence by the recognition helix is considered the well understood mechanism for this. However, differential affinity for O(R)1, O(R)2 and O(R)3 is equally critical to the switch because it mediates opposing regulation of divergent promoters. Site specificity at this second level is less well understood. Conformational adaptation by both the repressor and the different operators appears to be important. To evaluate how subunit-subunit interactions are involved in this process, we investigated the effects on both dimer stability and operator binding of amino acid substitutions at the contacts between the symmetrically related helices-5 in the dimer interface. Substitutions for Tyr88 alter dimer stability and greatly perturb differential operator affinity, but generally do not affect operator versus non-operator specificity. The pattern of these effects suggests that the geometry of the face-to-face aromatic stacking interaction between symmetrically related Tyr88 in each subunit, a group in the dimer interface but far removed from the DNA binding interface, plays a critical role in operator discrimination. Conformational changes in the tertiary structure of the subunits appears to be involved. By contrast, the significant effect of I84S substitution is to greatly decrease affinity for all three operators. Presumably, the altered packing of the dimer interface causes a quarternary structural change that moves the two helix-turn-helix motifs out of register with successive DNA major grooves.