Bacillus cereus 569/H β-lactamase I: Structure-function relationship

Abstract

Various functional groups of β-lactamase I were modified using appropriate group specific reagents. Modification of five of the ten arginine residues and approximately fifteen of twenty-one lysine residues present in the protein could readily be achieved by reaction with diacetyl trimer and trinitrobenzene sulfonic acid respectively, without any adverse effect on catalytic activity. Reaction with N-bromosuccinimide revealed that two of the three tryptophan residues could be oxidized without impairment of enzymatic activity. Treatment with tetranitromethane resulted in the modification of two of the seven tyrosine residues of the protein with approximately 30% diminution in activity. Reaction of the enzyme with a water soluble carbodiimide resulted in a rapid inactivation, complete loss of activity being accompanied by the modification of five of the carboxylic functions. Conversion of all the four histidine residues of the enzyme to the corresponding N-carbethoxy derivatives had no effect on the catalytic function. All these observations suggest that chemical modification of the enzyme in the presence of substrate or its analog is essential for the identification and/or localization of functional groups participating in the catalytic mechanism.