Carboxyl Group Modification and the Activity of Lysozyme

• Published in: The Journal of biological chemistry 1969-01, Vol.244 (2), p.505-508
• Main Authors: Lin, T Y, Koshland, Jr, D E
• Format: Article
• Language: English
• Subjects: Animals; Aspartic Acid; Binding Sites; Chemical Phenomena; Chemistry; Chickens; Cyanides; Egg White; Glutamates; Muramidase; Sulfonic Acids
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(18)94459-5

Modification of the carboxyl groups in hen's egg white lysozyme by the carbodiimide-nucleophile procedure developed in this laboratory has shown that all of the carboxyl groups except glutamic 35 can be modified under normal assay conditions. The presence of the substrate protects the aspartic acid residue 52 so that an enzyme with over 50% activity is obtained in which all carboxyls except aspartic 52 and glutamic 35 have been converted to the [see PDF for equation] derivatives. Subsequent treatment after the removal of substrate leads to concomitant modification of aspartic 52 and loss of enzyme activity. These results eliminate all carboxyl residues except glutamic 35 and aspartic 52 as potential catalytic groups or essential binding groups. They add strong support to the hypothesis of Phillips and his coworkers, deduced from crystallographic studies, that these residues are involved in the catalytic action. All other carboxyl groups appear to be on the surface of the protein molecule in terms of accessibility to reagent but individual residues vary in reactivity both in the carboxyl activation step and in the subsequent nucleophilic displacement on the activated carboxyl.