NATURE OF AMINO ACID SIDE CHAINS WHICH ARE CRITICAL FOR ACTIVITY OF LYSOZYME

Chemical modification by use of selective reagents has been applied to the side chains of lysine, histidine, tyrosine, and carboxyl residues in lysozyme. The properties of the lysozyme derivatives have been monitored by measuring (a) their ability to bind chitotriose and (b) their catalytic efficiency for hydrolysis of chitotriose or Micrococcus lysodeikticus cells. Thus, effects of chemical modification on binding properties or catalytic properties have been distinguished. In thismanner it has been shown that neither lysine, histidine, nor tyrosine residues play a role in catalysis by lysozyme. Modification of carboxyl groups, however, by various chemical treatments abolishes catalytic activity. A new reagent for preferential esterification of protein carboxyl groups has been employed which has made it possible to isolate two singly esterified lysozyme derivatives. Oneof these derivatives has been shown to contain a labile carboxyl ester which is most likely at or close to the strong binding site for chitotriose. The other derivative has been shown to contain a single carboxyl ester and to be essentially inactive against both M. lysodeikticus and chitotriose as substrates, while retaining the ability to effect good binding of the trisaccharide. © 1969, American Chemical Society. All rights reserved.