Abstract
A method for the rapid modification under mild conditions of carboxyl groups in proteins has been developed. The method involves the activation of the carboxyl group by a water-soluble carbodiimide and the subsequent reaction of the activated carboxyl group with a nucleophile such as glycine methyl ester. The kinetics of the reaction indicates that there are limits to the variation of carbodiimide and nucleophile when quantitative modification is desired, but that a wide variety of reagents can be used if quantitative reaction is not essential. Thus, variation in the structure of the carbodiimide can affect the carboxyl groups activated, and variation in the charge, size, and chemical and spectral properties of the nucleophile can alter the type of modification at a specific carboxyl group. The reaction proceeds equally well in high concentrations of urea or guanidine hydrochloride. The method appears to be of wide utility for analytical purposes and structure-function correlations.
Highlights
Khorana [12] has postulated that the initial phase in the reaction of a carboxylic acid with a water-soluble carbodiimide involves the formation of an 0 acylisourea (Equation 1)
Support for an initial step in accord with Equation 1 was obtained by performing the equivalent reaction with a phenol in order to obviate the difficulties caused by rearrangements of the initial product which might occur with a carboxylic acid
The results indicate that the carboxylic acid groups in a protein which has been completely unfolded are approximately equal in reactivity to each other and to the carboxyl groups of small model compounds
Summary
Mechanism of Reaction of Carbodiimides with Carboxylic Acids - the main purpose of this study was to perfect a quantitative method, the design of the procedure required kinetic determinabons, which have revealed some features of the reaction of water-soluble carbodiimides
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