ABSTRACT
Two metal ion binding sites are conserved in metallo-beta-lactamase from Aeromonas hydrophila. The ligands of a first zinc ion bound with picomolar dissociation constant were identified by EXAFS spectroscopy as one Cys, two His and one additional N/O donor. Sulfur-to-metal charge transfer bands are observed for all mono- and di-metal species substituted with Cu(II) or Co(II) due to ligation of the single conserved cysteine residue. Binding of a second metal ion results in non-competitive inhibition which might be explained by an alternative kinetic mechanism. A possible partition of metal ions between the two binding sites is discussed.
Subject(s)
Aeromonas hydrophila/enzymology , beta-Lactamases/chemistry , Aeromonas hydrophila/genetics , Binding Sites , Cobalt/chemistry , Copper/chemistry , Imipenem/chemistry , Kinetics , Spectrum Analysis , Zinc/chemistryABSTRACT
The most widely used inactivators of active-site serine beta-lactamases behave as substrates of four class B metallo-beta-lactamases, but the efficiency of the catalytic process can vary by several orders of magnitude. A comparison of the kinetic parameters for the alpha and beta isomers of 6-iodopenicillanic acid shows that there is no general preference for the alpha isomer and that the efficient hydrolysis of imipenem by these enzymes must rest on other factors.
