Abstract
125I-Labeled derivatives of the β-lactam antibiotics cephalexin, cephradine, cefaclor and 6-α-aminopenicillanic acid have been obtained by reacting these compounds with (125I)-Bolton-Hunter reagent. The following target proteins were found in Escherichia coli: (1) The derivatives of cephalexin, cefaclor and cephradine preferentially interact with the high molecular weight penicillin binding proteins (PBP1a and PBP1b); (2) The 125I-derivative of 6-α-aminopenicillanic acid is preferentially bound by the low molecular weight penicillin binding proteins 4 and 5/6. The iodinated derivatives showed a very high affinity of binding to their target proteins with apparent half-saturating concentrations in the nano-molar range.
