Studies on the Relationship of Protein Binding and Gel-Affinity of Antibiotics Including Penicillins

Chromatography of Penicillins, Penicilloates, and Penicilloylamides on Dextran Gels

“…A rich array of sidechain differences is found in the commercially available penicillins, and derivatives can be prepared in which only the nuclear structure is altered, as represented by the penicilloates. As observed in these experiments and those of Murakawa and colleagues (22), the penicillins and their derivatives do not behave identically in dextran gel chromatography. Each of the penicillins examined had a unique partition coefficient, which was not predictable from its molecular weight, and the penicilloic and penicilloylamide derivatives which were examined differed substantially from their precursor in their partition behavior.…”

“…Electrostatic effects can be abrogated by saturation of the ion-exchange sites with rather trivial amounts of NaCl incorporated into gel, solute, and eluting buffers, as was done in our experiments. In the absence of electrostatic effects, it is apparent from our data and that of Murakawa et al (22) that adsorption of penicillin to gel is the principal determinant governing the behavior of most intact penicillins on highly crosslinked dextran gels. Furthermore, these adsorptive effects are attributable to the side-chain structure, and when the nucleus is intact the side-chain structure can be used to predict relative elution positions and KD values.…”

“…Electrostatic effects are due to ionized groups in the dextran (12), which exert maximal effect on charged solutes in deionized water (13,18,23). The KD values of penicillins in deionized water are substantially reduced over KD values observed in the presence of NaCl (22), presumably due to electrostatic repulsion attributable to the C, carboxyl and other ionizable substituents. Electrostatic effects can be abrogated by saturation of the ion-exchange sites with rather trivial amounts of NaCl incorporated into gel, solute, and eluting buffers, as was done in our experiments.…”

“…Although the behavior of penicillins in dextran gel chromatography may be explained on several grounds, the phenomena observed appear to have predictive value for the behavior of penicillins in other interactions, notably protein binding (22). Recent studies by Hsu et al (16) suggest that the interacting site on proteins is hydrophobic in character and that differences in binding constants are related to the hydrophobic or hydrophilic nature of substituent functions on the penicillin side chain.…”

“…In the course of their studies, some data on chromatography of monomer penicillins was accumulated, but no systematic examination of the factors influencing their chromatographic behavior has been published. Recently, Murakawa et al (22) have compared the binding of different penicillins to proteins with their gel binding characteristics.…”