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At least 19 recordsLinked to original sources
PubMed1990

Thermodynamics of information transfer between subunits in oligomeric enzymes and kinetic cooperativity. 2. Thermodynamics of kinetic cooperativity.

The principles of structural kinetics allow one to define the thermodynamic conditions that are sufficient to generate a certain type of kinetic behavior. If subunits are loosely coupled, that is if no quaternary constraint exists between them, the kinetic behavior of the polymeric enzyme is qualitatively defined by the behavior of an ideal dimer. The nature and the extent of the kinetic cooperativity are defined by the energy of interaction, delta G rho, between two subunits. This energy of interaction is that of an ideal dimer relative to that of the A2 and B2 states. This thermodynamic formulation of a given type of cooperativity holds whatever the degree of polymerization of the enzyme. Under these conditions of loose coupling between subunits, positive kinetic cooperativity cannot be associated with any sigmoidicity of the rate curve. The range of energy coupling where positive kinetic cooperativity must, of necessity, be observed becomes more and more narrow as the number of subunit interactions is increased. This range, however, is independent of the number of subunits. The same situation is not observed for negative cooperativity which appears to be independent of both the number of subunits and the number of subunit interactions. If the subunits are tightly coupled, that is if quaternary constraints exist between them, three thermodynamic parameters, delta G' rho, delta G lambda, delta G mu, are required to define the nature of kinetic cooperativity. delta G' rho is the free energy of an ideal strained dimer relative to that of strained A2 and B2 states. delta G lambda and delta G mu represent the difference of strain energies between conformations A and B and B and B relative to that existing between conformations A and A. One may determine in the parametric space (delta G' rho, delta G lambda, delta G mu) the boundaries between the sufficient conditions that generate a certain type of cooperativity and the lack of these conditions. The kinetic parameters of the rate equation are not all independent. A number of constraint conditions exist between them which depend upon the subunit design of the polymeric enzyme. The existence of these constraint conditions may be diagnostic of a certain type of subunit interactions.

Enzymes↗
PubMed1978

Studies of the chemo-mechanical conversion in artificially produced streamings. III. Dynamic cooperativity--a new cooperativity in actomyosin systems with a polarized arrangement of F-actin.

The order--disorder phase transition in the chemo-mechanical process in our streaming system, which was reported in the preceding paper [Yano, M. & Shimizu, H., J. Biochem, 84, 1087--1092], was studied in detail. Starting from the hypothesis that a new type of cooperativity, dynamic cooperativity, is present in the elementary cycles of the chemo-mechanical conversion, quantitative and consistent agreement was obtained between the theoretical and experimental data on the temperature dependences of the streaming velocity and the ATPase activity, including the presence of the phase transition. The hypothesis was also supported by observations of the temperature dependence of the ATPase activity in resisted streaming. The physical and physiological significance of dynamic cooperativity is considered. It is shown that dynamic cooperativity arises in actomyosin system which have a polarized arrangement of F-actin by directed streaming of the solution, because the rate of the elementary cycle can be accelerated by the streaming. Furthermore, dynamic cooperativity is the key mechanism of self-organization of a dynamical order such that in ordered motions, and is one of the essential conditions for the direct conversion of the chemical energy of ATP to the mechanical energy of ordered and directed motion.

Actins↗
PubMed1985

Cooperative and non-cooperative processes of apparent movement of random-dot cinematograms.

In this study, we investigated the cooperative and non-cooperative models of stereopsis on apparent movement of the short-range process using spatial frequency filtered random-dot cinematograms. Our results showed that when spatial frequencies were below 4 cycles/degree, maximum displacement (dmax) was decreasing (linearly) with increasing mean frequencies, but at 4 cycles/degree and above dmax stayed constant. For low frequencies, non-cooperative models such as Marr and Poggio's could explain these findings, but not for frequencies above 4 cycles/degree. However, in a previous study we found that the average cooperative neighbourhood for apparent movement of the short-range process is 15 arc min. This fortuitous agreement on 4 cycles/degree could suggest that dmax being constant at frequencies above 4 cycles is related to a cooperative process.

Depth Perception↗
PubMed1977

Cooperativity concepts in protein binding models--problems of cooperativity definition, detection, identification and measuring.

Cooperativity in protein-ligand binding cannot yet be treated as a urinary phenomenon (neither in investigating nor in modelling), although imaginable to rest upon some few general principles only. Knowledge of atomic details of protein-ligand interactions is still limited. Instead of a physico-chemical explanation and definition of cooperativity, a series of schematic concept has been established throughout the literature. Some dominating or merely observable features are isolated and intermixed with plausibly invented mechanistic details. These cooperativity concepts are put together and partly generalized here. From comparing these concepts with the state of binding theory on the one hand and with the nature of measured binding data on the other, some problems of understanding cooperative effects and of detecting, measuring and identifying them are pointed out. For special cases, suitable criteria and measures are recommended and graphic and mathematical techniques discussed. The limited significance and generality of current cooperativity terms is emphasized. Some different levels of understanding have to be distinguished.

Ligands↗
PubMed1985

Cooperative behaviour in monomeric enzymes. Change of negative to positive cooperativity by effect of a ligand.

Three steady-state models were analysed to see if they could reproduce the following kinetic characteristics in a monomeric enzyme with two substrates: a) kinetic cooperativity with respect to the first substrate but not to the second; b) modulation of the kinetic cooperativity for the first substrate by the concentration of the second; c) change in the sign of the kinetic cooperativity at very low concentrations of the second substrate. A slow transition model previously proposed for vertebrate "glucokinase" (hexokinase D), model I, (Olavarría et al., 1982) was able to reproduce characteristics a and b, but never c. The "mnemonical" model (Ricard et al., 1974), model II, also reproduced characteristics a and b, and failed to reproduce c. Thus when observations were performed at concentrations of the first substrate around K0.5 it was possible to observe a decrease in the Hill coefficient (h) relative to the decrease in the concentration of the second substrate, but values lower than 1.0 were never obtained. At extremely high substrate concentrations, the second substrated did not affect the cooperativity of the enzyme for the first substrate. Model III was similar to Model I, but it was considered that only the enzyme conformer with the higher affinity for the first substrate was catalytically active. With this model it was possible to change positive cooperativity into negative if the second substrated altered the frequency of the conformational transition.

Binding Sites↗
PubMed1983

Cooperative lipid activation of (Na+ + K+)-ATPASE as a consequence of non-cooperative lipid-protein interactions.

Lipid activation data for (Na+ + K+)-ATPase (Ottolenghi, P. (1979) Eur. J. Biochem. 99, 113-131) have been subjected to a regression and fitting analysis based on a recent kinetic model (Sandermann, H. (1982) Eur. J. Biochem, 127, 123-128). The observed kinetic cooperativity could be generated from strictly non-cooperative binding events involving the known number of 30 boundary lipid-binding sites per ATPase monomer. Apparent lipid dissociation equilibrium constants of between 0.3 and 5 microM were obtained, enzyme activity being associated only with the fully lipid-substituted enzyme and enzyme-lipid complexes with less than six unoccupied lipid-binding sites. The enzyme appeared to operate close to a maximum of cooperativity.

Animals↗
PubMed1978

Cooperative and non-cooperative binding of large ligands to a finite one-dimensional lattice. A model for ligand-oligonucleotide interactions.

A combinatorial approach is employed to calculate exact expressions for the extent of binding to a finite one dimensional lattice of ligands which cover more than one lattice site. The binding may be either cooperative or non-cooperative. It is found that the assumption of an effectively infinite lattice is generally a good one, except with relatively low concentrations of strongly cooperative ligands. An approach to analyzing experimental data is suggested which makes explicit use of the lattice length dependence of binding to extract more information about the binding parameters than can be obtained using the infinite lattice approximation. It is shown that irreversible binding cannot be viewed as a limiting case of reversible binding. The reasons for this difference are discussed, and expressions for the extent of irreversible binding are derived.

Binding Sites↗
PubMed1990

[The importance of cooperation in primary health care. Utilization of physicians' services and home nursing services during different degrees of cooperation].

A study carried out in the county of Vestfold in the spring of 1989 clearly showed how cooperation between doctor and nurse influenced the level and quality of care provided by doctors to patients nursed at home. Good cooperation coincided with high quality health services, and ensured rational use of resources in relation to the patients' needs. The study showed that the quality and frequency of cooperation between doctor and nurse are of utmost importance for the service given to the patients.

Community Health Nursing↗
PubMed1988

Evaluation of pathology review of malignant lymphomas and Hodgkin's disease in cooperative clinical trials. The Eastern Cooperative Oncology Group experience.

Although central expert pathology review for quality assurance in cooperative clinical trials involving malignant lymphomas and Hodgkin's disease was put in place by the NCI two decades ago, its impact upon patient eligibility for given treatment protocols has never been assessed. We reviewed diagnoses from contributing pathologists, the Eastern Cooperative Oncology Group (ECOG) review pathologists and the Pathology Panel for Lymphoma Clinical Studies in 2019 cases from 14 ECOG protocols. Although we found high rates of disagreements in diagnoses, the vast majority of these represented differences which did not impact on protocol eligibility. A total of 221 cases (10.9%) were excluded from protocols, representing a range of 2.8 to 36.7% of cases per protocol. Eighty-six percent of the exclusions resulted from the initial review by the ECOG hematopathologists. Our data indicate that while central pathology review is mandatory for quality assurance in malignant lymphoma (ML) and Hodgkin's disease (HD) protocols, a two-tier review mechanism is not necessary for adequate quality control.

Clinical Trials as Topic↗
PubMed1976

Cooperative interactions of tetrahydrofolate with purified pig kidney serine transhydroxymethylase and loss of this cooperativity in L1210 tumors and in tissues of mice bearing these tumors.

Serine transhydroxymethylase (5,10-methylenetetrahydrofolate: glycine hydroxymethyl transferase, EC 2.1.2.1) purified 200-fold from pig kidneys showed cooperative interactions with tetrahydrofolate with a Hill coefficient (n value) of 3.9 and a substrate concentration at 50% of maximum velocity, the S(0.5) value, of 0.5 mM. The enzyme in mouse liver and kidney homogenates also showed cooperative interactions with tetrahydrofolate. However, the enzyme obtained from L1210 solid tumors of mice, and from livers and kidneys of mice inoculated with L1210 cells exhibited hyperbolic saturation kinetics and gave a Michaelis constant, Km, value of 0.5 mM for tetrahydrofolate. The interaction of serine with the enzyme from pig kidney, from tissues of normal or tumor-bearing mice, or from L1210 tumors was hyperbolic with a Km of 0.9 mM. The specific activities of the enzyme in the L1210 tumor and in mouse liver were 10-fold higher than in pig or mouse kidney. There was no significant change in the levels of the enzyme in mouse liver and kidney on inoculation with L1210 cells. These results suggest that a tumor can bring about biochemical changes in tissues that are distal to the tumor.

Allosteric Regulation↗
PubMed1976

Cooperation across the histocompatibility barrier: H2d T cells primed to antigen in an H-2d environment can cooperate with H-2k B cells.

H-2d spleen cells derived from either tetraparental or semiallogeneic radiation bone marrow chimeras can be primed to antigen within H-2d recipients to generate helper T cells capable of cooperating in a secondary response with equal efficiency with H-2d or H-2k B cells. Thus it would seem that the cooperative act between T and B cells does not require that the T cell interacts with its target B cells by either cell interaction genes or via an altered self mechanism involving both antigen and the target B-cell I-region products. This does not preclude a requirement for associative recognition or altered self in the interaction of helper T cells with accessory cells.

Animals↗
PubMed1988

Rat liver glycine methyltransferase. Cooperative binding of S-adenosylmethionine and loss of cooperativity by removal of a short NH2-terminal segment.

Rat liver glycine methyltransferase, a homotetramer, exhibits sigmoidal rate behavior with respect to S-adenosylmethionine (Ogawa, H., and Fujioka, M. (1982) J. Biol. Chem. 257, 3447-3452). The binding experiment shows that the sigmoidicity observed in initial velocity kinetics is explained by the cooperative binding of S-adenosylmethionine to the catalytic sites residing on each subunit. Limited proteolysis of glycine methyltransferase with trypsin in the presence of S-adenosylmethionine yields an enzyme lacking the NH2-terminal 8 residues. The proteolytically modified enzyme retains a tetrameric structure. The truncated enzyme shows no cooperativity with respect to S-adenosylmethionine binding and kinetics. It has values of Vmax and Km for glycine identical to those of the native enzyme, but a 3-fold lower [S]0.5 value for S-adenosylmethionine. The proteolytic modification is without effect on the circular dichroism and fluorescence spectra. Furthermore, the protein fluorescence of the modified enzyme is quenched upon addition of S-adenosylmethionine to the same extent as observed with the native enzyme. These results suggest that a short NH2-terminal segment, which lies outside the active site, is important for communication between subunits.

Animals↗
PubMedDate not supplied

[Model for tobacco mosaic virus assembly in vitro: specific dislocation by cooperative single-letter purine recognition and non-cooperative RNA "locking" between subunit layers].

A model of the molecular mechanism of tobacco mosaic virus (TMV) assembly in vitro is proposed. The model is based on the assumption that on interaction of TMV RNA chain with a double protein disk two different types of structural alterations occur in the protein subunits: "dislocating alterations" leading to screw dislocation of the disk into a helix fragment and "locking alterations" leading to locking of the RNA chain between the subunits layers. During initiation of TMV assembly the dislocating alterations occur cooperatively in all subunits of the disk as a result of specific interaction of purines (guanines) in the middle (horizontal) position of every trinucleotide unit with the 32--39 loop of the TMV protein molecule. Locking alterations are induced non-cooperatively by phosphate groups and lateral (vertical) bases of trinucleotide units. The sequence of events during TMV assembly in vitro and the role of topological factors in this process are discussed.

Models, Biological↗
PubMed1979

[Medical development cooperation in the Confederation. The international framework and the important place of public health in Swiss development cooperation].

The systematic organization of health services in the developing countries to benefit the majority of the population is seen as an important contribution toward the general economic and social development of these countries. This view is uncontested today, but was given less importance in the early years of Swiss development aid. The Swiss Development Cooperation's support of health services is now integrated into its overall program to satisfy the basic needs of the people of the developing countries.

Developing Countries↗
PubMed1985

A computerized approach towards the estimation of binding parameters to characterize cooperative and non-cooperative multicomponent ligand-receptor interactions.

A mathematical model has been developed to analyse multicomponent ligand-receptor interaction data directly from binding experiments without resorting to approximations such as linearization. This approach may be applied to analyze binding data for radioreceptor systems involving thyroid and steroid hormones, and drugs on neurotransmitters. Affinity constants, maximal binding capacity, cooperativity and nonspecific binding may be calculated for multiple binding systems.

Adipose Tissue↗
PubMed1987

Two-step ligand binding and cooperativity. A model to describe the cooperative binding of myosin subfragment 1 to regulated actin.

The binding of actin to myosin subfragment 1 (S1) has been shown to occur as a two-step reaction. In the first step actin is weakly bound and then the complex isomerizes to the "rigor type" acto-S1 complex (Coates, J. H., A. H. Criddle, and M. A. Geeves, 1985 Biochem. J., 232:351-356). We propose here a model in which troponin/tropomyosin (Tn/Tm) controls the actin-S1 interaction by inhibiting the isomerization step. In this model the (actin)7 Tn/Tm unit is assumed to exist in two states: open and closed. S1 can bind to either of the two states but only the open form allows the isomerization reaction to take place. We demonstrate that this model can account for the cooperative binding of S1 and S1 nucleotide complexes to actin. The model provides a way of integrating both the effects of calcium and nucleotide on actin-S1 interactions.

Actins↗
PubMed1975

Antigen-specific T-cell factor in cell cooperation. Mapping within the I region of the H-2 complex and ability to cooperate across allogeneic barriers.

Further mapping of the mouse T-cell factor specific for poly(Try,Glu)-polyD-LAla--polyLys is reported. It is shown to be a product of the I-A subregion of the H-2 complex by the use of antisera either raised specifically against or made specific, by absorption, for different regions of the H-2 complex. The factor cooperates across allogeneic barriers, e.g., when factor produced by one strian is combined with bone marrow cells of other H-2 incompatible strains.

Animals↗