States of Amino Acid Residues in Proteins

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Abstract
A water soluble carbodiimide, EMPC, was applied in the presence of glycine ethylester to acetylglycine and proteins, and was found to be a reagent suitable for discrimination of different states of carboxyl groups in the tertiary structures of proteins. One of the total two carboxyl groups in the bacitracin molecule, at least three of the six carboxyl groups in bovine insulin and six of the eleven carboxyl groups in egg white lysozyme [EC 3.2.1.17] were modified by the treatment with 40 mM EMPC for 3 hours at room temperature and no further reaction took place at higher EMPC concentrations. All of these carboxyl groups were modified when the proteins had been denatured with guanidine. The results obtained in these measurements were compared with previous modification data in view of the state discrimination of carboxyl groups.