Evidence for specific interaction of guanidine hydrochloride with carboxy groups of enzymes/proteins

Experimental evidence for the interaction of Gdn.HCl with carboxylate groups of the proteins is presented, for the first time, based on (i) the inhibition by low concentrations of Gdn.HCl of enzymes that are known to require essential carboxyl groups for their catalytic activity unaccompanied by structural changes in the protein and (ii) failure of the carboxyl-specific Woodward's reagent K to react specifically with the carboxyl groups of the proteins/enzymes pretreated with Gdn.HCl. The results demonstrate that the specificity and the reversibility of interaction of Gdn.HCl with carboxylate groups of proteins can be gainfully utilized for probing the functional role of carboxylate residues in the proteins.