An additional ionic bond suggested by molecular modelling of TEM-2 might induce a slight discrepancy between catalytic properties of TEM-1 and TEM-2 beta-lactamases

The plasmid-mediated TEM-1 and TEM-2 beta-lactamases are the most commonly encountered among Gram-negative bacteria. They belong to molecular class A, and differ by one amino acid at position 39: TEM-1 have a glutamine and TEM-2 a lysine. Kinetic parameters (k(cat) and K-m) and catalytic efficiency (k(cat)/K-m) of TEM-1 and TEM-2 beta-lactamases are slightly, but significantly different. For all antibiotics except methicillin and cefazolin, the catalytic efficiency values of TEM-2 are clearly greater than that of TEM-1. Molecular modelling of TEM-2, when compared to that of TEM-1, showed an additional ionic bond between Lys-39 and Glu-281.