title: Effect of albumin conformation on binding of phenylbutazone and oxyphenbutazone to human serum albumin.
abstract: The binding of phenylbutazone (I) and oxyphenbutazone (II) to human serum albumin over pH 6.9-9.3 was studied by difference spectrophotometry and equilibrium dialysis. At each pH tested, there was higher binding affinity of I to human serum albumin than II. Equilibrium dialysis showed that over the pH 7-8.2 range both agents had a single high-affinity site and several sites of lower affinity, with the highest binding constant and number of binding sites at pH 7.4 for both I and II. Both techniques showed that the affinity of both drugs to albumin was higher for the neutral form than for the basic form and this transition occurred in both cases around the neutral region (7-7.4). Both the ionized and unionized forms of I and II participated in the binding. In the neutral region, magnesium ion increased the affinity of both drugs to albumin while chloride ion decreased it slightly.
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002712:Chlorides; D003956:Dialysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008274:Magnesium; D010113:Oxyphenbutazone / Q000097:blood*; D010653:Phenylbutazone / Q000097:blood*; D011485:Protein Binding; D011487:Protein Conformation; D012709:Serum Albumin / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D002712:Chlorides; D012709:Serum Albumin; D010653:Phenylbutazone; D010113:Oxyphenbutazone; D008274:Magnesium