Simple Photometric Assay of β-Lactamase Activity

A simple photometric assay of beta-lactamase activity was developed. The method is based on a decrease in optical density at 620 nm caused by the formation of a penicilloic acid-iodine complex. The enzymatic reaction is instantaneously stopped by the addition of a concentrated iodine-tungstate solution. Data showing the time and concentration dependence of the reaction are presented. By varying both the time of the assay and the concentration of the enzyme, substrates of widely different V(max) values could be assayed. The assay is compared with other methods of determining beta-lactamase activity.