Characterization of Extracellular β-Lactamases from Penicillin G-Resistant Cells of Streptococcus thermophilus

Abstract

In this study, biochemical properties of two extracellular β-lactamases produced by penicillin-resistant Streptococcus thermophilus cells were investigated. Both β-lactamases showed specificity for penicillins but not for cephaloridins. The β-lactamases exhibited different affinities for penicillin G. The one with the higher molecular weight (FI) had a Km value of 3.44 μM and a Vmax value of 8.33 μmol/min/mg of protein, whereas the β-lactamase with the lower molecular weight (FII) had a Km value of 4.76 μM and a Vmax value of 3.13 μmol/min/mg of protein. Both β-lactamases were inhibited by iodine, copper sulfate, and iron sulfate but not by EDTA. The optimal pH ranged between 6 and 7, and the optimal temperatures were between 40 and 45°C for both enzymes.