title: [Quantum chemistry analysis of the mechanism of action of proteolytic enzymes. III. Proton transport in serine proteases].
abstract: The model system for the proton transfer on the amide atom of the substrate leaving group based on the existence of "charge relay system" in the serine type proteases was analysed by the CNDO/2 method. The unfitness of this model to explain the action mechanism of serine proteases was shown. The model system for proton transfer with the water molecule as the intermediate acceptor of the Ser-195 proton was suggested and analysed by the same method. The acylation activation barrier of this system was shown to localize on the stage of synchronous transfer of the Ser-195 alcoholic proton and the water molecule proton hydrogen bound to the His-57 N epsilon 2-atom on the water molecule oxygen atom and the N epsilon 2-atom, respectively. The protonation of substrate in the case of the model system with the water molecule as the intermediate acceptor of proton was demonstrated to begin before the completion of the tetrahedral intermediate substance and the protonated from of the tetrahedral intermediate was shown to form only. A hypothesis considering the role of this water molecule as the nucleophilic reagent on the deacylation stage is presented.
mesh_terms: D000081:Acetamides / Q000378:metabolism; D001692:Biological Transport; D010450:Endopeptidases / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism; D066298:In Vitro Techniques; D000432:Methanol / Q000378:metabolism; D008956:Models, Chemical; D011522:Protons; D011789:Quantum Theory; D012697:Serine Endopeptidases; D013379:Substrate Specificity
chemical_list: D000081:Acetamides; D007093:Imidazoles; D011522:Protons; D010450:Endopeptidases; D012697:Serine Endopeptidases; C018100:1-methylimidazole; C018595:N-methylacetamide; D000432:Methanol
vernacular_title: Kvantovo-khimicheskiĭ analiz mekhanizma deĭstviia proteoliticheskikh fermentov. III. Perenos protona v proteazakh serinovogo tipa.