beta-Lactamases are important enzymes, responsible for bacterial resistance against beta-lactam antibiotics. The enzymes from class A are the most common and the most intensively studied. Here we present our electronic structural study on the relationships between electrostatic interactions and chiroptical properties of three enzymes from class A in the following directions: (i) an integrated influence of environment and ionization state on the rotational strengths mechanisms of tyrosine chromophore in TEM-1 beta-lactamase; (ii) an effect of electrostatic environment on the mechanisms of aromatic rotational strengths in beta-lactamases from Streptomyces albus and Staphylococcus aureus. (C) 2008 Elsevier B. V. All rights reserved.