Influence of Blood Proteins on Biomedical Analysis. II. Interaction of Gliclazide with Bovine Serum Albumin

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The interactions of gliclazide, a potential hypoglycemic drug, with native and chemically modified bovine serum albumin (BSA) were studied by means of an equilibrium dialysis technique. The Scatchard plot for the interaction of gliclazide with native BSA was a hyperbola, suggesting the existence of two (or more) classes of gliclazide-binding sites on the BSA molecule (n₁=0.5, K₁=160×10³M^-1 ; n₂=4.5, K₂=4.4×10³M^-1). Total binding capacity (Σn_iK_i) for gliclazide-BSA binding was lower (99.8×10³M^-1) than that (190.7×10³M^-1) for tolbutamide. Modification of BSA with hydrogen peroxide, iodoacetic acid, iodoacetamide or 2-hydroxy-5-nitrobenzyl bromide lowered the binding affinity in the primary binding site or destroyed the binding site, and decreased the total binding capacity of gliclazide-BSA binding. Since the binding capacities of the primary and secondary binding sites varied upon modification of cysteine, methionine, histidine and tryptophan residues of the BSA molecule, it is possible that the binding sites are both closely associated with loops 1-4 of the BSA molecule.