[Nature of the intermediate compound formed during catalysis by pepsin]

The applicability of the free energies linearity principle to catalysis by pepsin may indicate that the mechanism of formation of a covalent pepsin intermediate with the second (amine or alcohol) part of the hydrolyzed substrate is a true one. The choice has been made from consideration of three possible types of mechanisms covalent binding, complex with a nonionized NH2-group and the absence of an activated intermediate.