RESUMO
Histamine is a primary mediator in allergic response and acts in concert with other agents to impact disease progression. Respiratory disorders such as asthma, rhinitis and dermatological conditions such as urticaria involve histamine along with other mediators. An antihistamine that possesses an additional property of counteracting the effects mediated by these other mediators should offer some therapeutic benefit over a selective antihistaminergic agent.
Assuntos
Antagonistas dos Receptores Histamínicos H1/farmacologia , Animais , Antagonistas de Receptor B2 da Bradicinina , Antagonistas dos Receptores Histamínicos H1/química , Humanos , Leucotrienos/metabolismo , Receptor B2 da Bradicinina/metabolismo , Receptores Histamínicos/metabolismo , Receptores de Taquicininas/antagonistas & inibidores , Receptores de Taquicininas/metabolismo , Receptores de Tromboxano A2 e Prostaglandina H2/antagonistas & inibidores , Receptores de Tromboxano A2 e Prostaglandina H2/metabolismoRESUMO
The binding cavity of histamine and histamine antagonists is explored using site directed mutagenesis of the human histamine H1 receptor and the amino acids involved in ligand binding are identified. Whereas Asp107 and Phe199 are important for both agonists and antagonists, two additional amino acids (Asn198 and Trp103) are required for efficient histamine binding. The binding site of antagonists is best defined as resulting from a strong ionic bond to Asp107, an orthogonal interaction between one of the aromatic rings with Phe199, and probably a hydrophobic interaction between the second aromatic ring and the lipophilic amino acids of the upper part of TMIV and TMV. This is consistent with structure-activity data of most described antagonists.
Assuntos
Antagonistas dos Receptores Histamínicos H1/farmacologia , Receptores Histamínicos H1/genética , Sequência de Aminoácidos , Animais , Antagonistas dos Receptores Histamínicos H1/química , Humanos , Dados de Sequência Molecular , Receptores Histamínicos H1/efeitos dos fármacosRESUMO
The comparative conformational analysis of four Substance P antagonists (NK1-) having different chemical structures allowed to formulate an hypothesis for a peptidic NK1 pharmacophore. The salient features of this pharmacophore (three aromatic groups and two carbonyl functions) belong to a beta-turn conformation. Thus, this kind of conformation might be the basis for the design of newer pseudo-peptidic and non-peptidic NK1 antagonists.
Assuntos
Antagonistas dos Receptores de Neurocinina-1 , Peptídeos/síntese química , Substância P/antagonistas & inibidores , Sequência de Aminoácidos , Dados de Sequência Molecular , Peptídeos/antagonistas & inibidores , Peptídeos/farmacologia , Conformação ProteicaRESUMO
Biosynthetic thiolase from Zoogloea ramigera was inactivated with a mechanism-based inactivator, 3-pentynoyl-S-pantetheine-11-pivalate (3-pentynoyl-SPP) where K1 = 1.25 mM and kinact = 0.26 min-1, 2,3-pentadienoyl-SPP obtained from nonenzymatic rearrangement of 3-pentynoyl-SPP where K1 = 1.54 mM and kinact = 1.9 min-1 and an affinity labeling reagent, acryl-SPP. The results obtained with the alkynoyl and allenoyl inactivators are taken as evidence that thiolase from Z. ramigera is able to catalyze proton abstraction uncoupled from carbon-carbon bond formation. The inactivator, 3-pentynoyl-SPP and the affinity labeling reagent, acryl-SPP, trap the same active site cysteine residue, Cys-378. To assess if Cys-378 is the active site residue involved in deprotonation of the second molecule of acetyl-CoA, a Gly-378 mutant enzyme was studied. In the thiolysis direction the Gly-378 mutant was more than 50,000-fold slower than wild type and over 100,000-fold slower in the condensation direction. However, the mutant enzyme was still capable of forming the acetyl-enzyme intermediate and incorporated 0.81 equivalents of 14C-label after incubation with [14C]Ac-CoA for 60 min. The reversible exchange of 32P-label from [32P]CoASH into Ac-CoA, catalyzed by the Gly-378 mutant enzyme, proceeded with a Vmax (exchange) 8,000-fold less than the wild type enzyme but at least 10-fold faster than the overall condensation reaction. These data provide evidence that Cys-378 is the active site base.