Thermodynamic parameters delta G degree, delta H degree and delta S degree of the binding equilibrium of eleven ligands (seven agonists and four antagonists) to the serotonin 5-HT3 receptor subtype ...have been determined by affinity measurements carried out on rat cortex membranes at six different temperatures (0, 10, 20, 25, 30, 35 degrees C) and van't Hoff plots. Affinity constants were obtained from saturation experiments of 3Hendo-N-(9-methyl-9-azabicyclo3.3.1non-3-yl)-1-methyl-1-H-indazole- 3- carboxamide (3HBRL 43694, a selective 5-HT3 ligand) or by its displacement in inhibition assays for the other compounds. Van't Hoff plots were essentially linear in the temperature range investigated, showing that the delta Cp degree of the binding equilibrium is nearly zero. Thermodynamic parameters are in the range 18 < or = delta H degree < or = 53 kJ mol-1 and 202 < or = delta S degree < or = 320 J K-1 mol-1 for agonists and -16 < or = delta H degree < or = 0 kJ mol-1 and 70 < or = delta S degree < or = 179 J K-1 mol-1 for antagonists indicating that agonistic binding is totally entropy-driven while antagonistic binding is relatively less entropy- and more enthalpy-driven in the -T delta S degree versus delta H degree plot the thermodynamic data are clearly arranged in separate clusters for agonists and antagonists, which, therefore, turn out to be thermodynamically discriminated. Experimental results are discussed according to the following main points: (i) the approximate linearity of the delta H degree versus delta S degree plot in terms of enthalpy-entropy compensation and (ii) the fact that delta Cp degree approximately equal to 0 for practically all membrane receptors at variance with most reactions involving biomacromolecules in solution. Finally, the phenomenon of thermodynamical discrimination is reviewed and found to occur in five distinct membrane receptorial systems.
The temperature dependence of the binding of β-carboline derivatives to the central benzodiazepine receptors was determined using
3H-Ro 15-1788, as a selective radioligand. The compounds chosen ...display a wide spectrum of efficacies ranging from inverse agonists to agonists through antagonists. Assays were performed at 0,10, 20, 25, 30, 35 °C in the absence and in the presence of 10 μM GABA. The temperature dependence of the affinity constants K
A =
1
K
D
or
1
K
i
is shown in the van't Hoff plots (ln K
A versus
1
T
) for each compound. Thermodynamic parameters ΔG °, ΔH ° and ΔS ° were determined by regression analysis of the plots which were linear in the range of temperatures investigated. Moreover, their slopes were systematically positive indicating that the binding of the compounds analyzed to benzodiazepine receptors is essentially enthalpy-driven both in the presence and in the absence of GABA. We verified that the ratio of affinity constant values in the presence and absence of GABA 10 μM (GABA ratio) (< 1 for inverse agonists, = 1 for antagonists, >1 for agonists), strongly correlates with the corresponding differences of ΔH ° and ΔS ° values obtained for each compound in the absence and in the presence of GABA. These results suggest that binding thermodynamic analysis of BDZ receptor ligands, in the presence and in the absence of GABA, permits to discriminate inverse agonists from antagonists, and agonists.
Security Requirements Engineering (SRE) deals with the elicitation and analysis of security needs to specify security requirements for the system-to-be. In previous work, we have presented STS-ml, a ...security requirements modelling language for Socio-Technical Systems (STSs) that elicits security needs, using a goal-oriented approach, and derives the security requirements specification based on these needs. Particularly, STS-ml relates security to the interaction among actors in the STS. In this paper, we present STS-Tool, the modelling and analysis support tool for STS-ml. STS-Tool allows designers to model a STS at a high-level of abstraction, while expressing security needs over the interactions between the actors in the STS, and derive security requirements in terms of social commitments - promises with contractual validity - once the modelling is done.
We address the challenge of requirements engineering for sociotechnical systems, wherein humans and organizations supported by technical artifacts such as software interact with one another. ...Traditional requirements models emphasize the goals of the stakeholders above their interactions. However, the participants in a sociotechnical system may not adopt the goals of the stakeholders involved in its specification. We motivate, Protos, a requirements engineering approach that gives prominence to the interactions of autonomous parties and specifies a sociotechnical system in terms of its participants' social relationships, specifically, commitments. The participants can adopt any goal they like, a key basis for innovative behavior, as long as they interact according to the commitments. Protos describes an abstract requirements engineering process as a series of refinements that seek to satisfy stakeholder requirements by incrementally expanding a specification set and an assumption set, and reducing requirements until all requirements are accommodated. We demonstrate this process via the London Ambulance System described in the literature.
The 2-amino-benzoylthiophene derivatives LUF 5468 (2-amino-4-ethyl-5-methyl-3-thienyl)3-(trifluoromethyl)phenylmethanone and LUF 5484 (2-amino-4,5,6,7-tetrahydrobenzo
...bthiophen-3-yl)(3,4-dichlorophenyl)methanone have been shown to allosterically enhance the adenosine A
1 receptor agonist binding. We report a thermodynamic analysis of the agonist affinity obtained at human adenosine A
1 receptors, in the presence and absence of LUF 5468 and LUF 5484. Moreover, an analysis of the temperature dependence for association and dissociation rates of
N
6-cyclohexyladenosine (CHA) binding was performed in the absence and presence of LUF 5484. Thermodynamic data were obtained by affinity measurements performed at different temperatures followed by van't Hoff analysis. The results indicate that the agonist binding is always totally entropy-driven, and that the modulators contribute to decrease the Δ
G°
, Δ
H°
and Δ
S°
values. It is concluded that the enhancers are able to increase the non-bonded interactions of the binding site with agonists as CHA,
N
6-cyclopentlyladenosine (CPA), 2′-methyl-
N
6-cyclopentyladenosine (MeCPA) and 2-chloro-2′methyl-
N
6-cyclopentyladenosine (MeCCPA).
The thermodynamic parameters delta G degrees, delta H degrees and delta S degrees of the binding equilibrium of serotonin to 5-HT1A, 5-HT2A and 5-HT3 rat-brain membrane receptors have been determined ...by means of affinity constant measurements at six temperatures in the range 0 -35 degrees C and van't Hoff plots. At variance with 5-HT1A and 5-HT3, the binding at the 5-HT2A receptors is strongly endothermic and entropy-driven. Comparison with the results obtained by other authors on 5-HT2A receptors in rats and humans suggests that the observed differences can be explained by a single amino acid difference in the receptor sequence between these two species.
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