A comparative study of the binding characteristics of ceftriaxone, cefoperazone and cefsulodin to human serum albumin.

The binding to human serum albumin of three cephalosporins of pharmacological interest: cefoperazone, ceftriaxone and cefsulodin was studied by ultrafiltration and differential scanning calorimetry methods. The identification of the binding sites in albumin was also performed using probes for the so-called sites I, II, bilirubin and fatty acids binding sites. Albumin showed two types of binding sites for cefoperazone and ceftriaxone, while for cefsulodin it showed a single type of binding site. The affinity values were: 5.6 10(4) M-1 and 3.1 10(4) M-1 for cefoperazone and ceftriaxone respectively, while cefsulodin showed low affinity (3.8 10(2) M-1). It was found that only cefoperazone interacted in a slight way with site I on serum albumin, while site II and the bilirubin binding site have capacity of binding the three cephalosporins assayed. Ceftriaxone and cefoperazone showed capacity to bind to the fatty acids binding site on albumin. These cephalosporins increased the thermal stability of the protein, suggesting that these ligands are favouring the compact structure of the native form of the protein more than the unfolded form.