Chemical Derivatives of dhymotrypsinogen

The reactions of a-chymotrypsinogen with carbon disulfide and with 0-methylisourea have been reported from this laboratory previously (1,2). The present report concerns the reaction of this protein with a new acylating agent, N-acetyl-nn-homocysteine thiolactone. The use of the thiolactone for the introduction of sulhydryl groups into proteins was fist suggested by Benesch and Benesch (3,4) who carried out exploratory studies with glycine, glycylglycine, and gelatin. The relatively mild conditions employed for these reactions indicated that the thiolactone would acylate amino groups of proteins without damaging the native structure. By analogy with acetic anhydride, one would expect acylation to be directed specifically toward amino groups. Beaction of a-amino groups could be favored over reaction of e-amino groups by control of pH and, consequently, the degree of ionization of amino groups, as was done in reactions with carbon disulfide (1). The aim of the present work was to find experimental conditions for the synthesis and isolation of the monoacylated derivative of cu-chymotrypsinogen in which only the single a-amino group was acylated. Studies of the protein were preceded by experiments on the hydrolysis of the thiolactone and on aminolysis by model compounds, diglycylglycme and e-amino caproic acid, at various pH values. The reaction of a-chymotrypsinogen with thiolactone proved to be more complicated than anticipated. Chromatography on columns of carboxymethyl cellulose led to the separation of the reaction product into a number of components, some of which have been characterized.