A comparative study of class-D beta-lactamases.
Three class-D beta-lactamases (OXA2, OXA1 and PSE2) were produced and purified to protein homogeneity. 6 beta-Iodopenicillanate inactivated the OXA2 enzyme without detectable turnover. Labelling of the same beta-lactamase with 6 beta-iodo[3H]penicillanate allowed the identification of Ser-70 as the active-site serine residue. In agreement with previous reports, the apparent M(r) of the OXA2 enzyme as determined by molecular-sieve filtration, was significantly higher than that deduced from the gene sequence, but this was not due to an equilibrium between a monomer and a dimer. The heterogeneity of the OXA2 beta-lactamase on ion-exchange chromatography contrasted with the similarity of the catalytic properties of the various forms. A first overview of the enzymic properties of the three 'oxacillinases' is presented. With the OXA2 enzyme, 'burst' kinetics, implying branched pathways, seemed to prevail with many substrates.
Laboratoire d'Enzymologie, Université de Liège, Belgium.
P
P
Ledent
X
X
Raquet
B
B
Joris
J
J
Van Beeumen
J M
JM
Frère
D001665:Binding Sites; D002384:Catalysis; D002846:Chromatography, Affinity; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D007700:Kinetics; D010397:Penicillanic Acid / Q000378:metabolism / Q000031:analogs & derivatives; D010957:Plasmids; D012694:Serine / Q000378:metabolism; D013379:Substrate Specificity; D065093:beta-Lactamase Inhibitors; D001618:beta-Lactamases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
D065093:beta-Lactamase Inhibitors; D012694:Serine; D010397:Penicillanic Acid; C031528:6-iodopenicillanic acid; D001618:beta-Lactamases