Modification of Protein Properties by Change in Charge.

Succinylated derivatives of bovine chymotrypsinogen A and α-chymotrypsin were prepared by treatment of the native proteins with succinic anhydride; 60% of the 6-amino groups of the 13 lysine residues form stable succinylated products. The large negative charge at neutral pH is reflected in electrophoretic and titration behavior but absorption spectra, rotatory-dispersion spectra and reversible unfolding behavior indicate that the succinylated species are conformationally similar to the parent proteins. Succinylated chymotrypsin is active as an esterase with N-acetyl-L-tryptophan ethyl ester with a small decrease in the maximum-velocity parameter. The pH dependence suggests that three ionizing groups influence catalytic behavior. The apparent pK_a values analyzed in terms of three groups are shifted relative to α-chymotrypsin. Thermal-unfolding studies of succinylated chymotrypsinogen demonstrate the presence of substrates near pH 7 but is consistent with two-state behavior at other pH values. [ABSTRACT FROM AUTHOR]