[pH dependence of tryptophan ethyl ester hydrolysis].

The dependence of the rate of spontaneous hydrolysis of tryptophan ethyl ester within a wide range of pH (4,6-10,3) was studied. This dependence was found to differ from other dependences, i.e. within the pH range of 4,6-7,0 the value of the rate constant is practically independent on pH. In order to describe the dependence obtained a general pattern of hydrolysis was postulated and the kinetic parameters of individual elementary reactions were determined. The rate constants for the hydrolysis of the amino acid with a non-protonated amino group of ester was calculated using the literary values for the rate constants of carboxylic acid hydrolysis. The obtained values of the second order rate constants for the alkaline hydrolysis of non-protonated and protonated forms of tryptophane ester (k4 and k5) are 1,1 and 79 M-1 s-1, respectively; those for the hydrolysis of the protonated form of the substrate (k3) are 1,0.10(-5) M-1 s-1. The role of spontaneous (non-enzymatic) hydrolysis in stereoselective cleavage of amino acid esters is discussed.