title: The alkaline transition of swine pepsinogen.
abstract: At alkaline pH, swine pepsinogen is reversibly inactivated in a transition which involves the cooperative release of two protons from the molecule and is governed by a pK = 9. Stopped flow kinetic studies on the absorbance changes accompanying this reaction show that it can be resolved into two steps, with increasing pH; a slow conformational change, whose amplitude follows the ionisation curve of one group of pK = 9.9, followed by a rapid pH dependent conformational change, linked to a group of pK = 8.2. The pH dependence of the rate of the slow step is interpreted to show the presence of a protonated group which cannot ionise in the neutral form of the zymogen, but is in slow equilibrium with a form where it titrates with a pK 6.8. At the same time, a histidine in the amino terminal region of the protein becomes reactive to diethyl pyrocarbonate, suggesting this to be the group which triggers the reaction.
mesh_terms: D000818:Animals; D004047:Diethyl Pyrocarbonate; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010435:Pepsinogens; D011485:Protein Binding; D011487:Protein Conformation; D013552:Swine
chemical_list: D010435:Pepsinogens; D004047:Diethyl Pyrocarbonate