HUMAN SERUM-ALBUMIN CONFORMATIONAL-CHANGES AS INDUCED BY TENOXICAM AND MODIFIED BY SIMULTANEOUS DIAZEPAM-BINDING

The binding of tenoxicam to human serum albumin has been shown by affi nity chromatography proton titration and equilibrium dialysis to be de pendent on the neutral to basic conformational change of the protein. The influence of diazepam on the interaction was also investigated usi ng the same techniques, suggesting that diazepam increases the associa tion of tenoxicam to albumin. Affinity chromatography revealed that th e reciprocal effect also occurs. Displacement studies indicated that d iazepam causes a significant increase in the affinity of tenoxicam to its main binding site, albumin site I, which is different from the dia zepam site (site II). Tenoxicam seemed to cause an allosteric change i n the conformation of the protein during its own binding, as did warfa rin. The mechanism of this effect was a pH-dependent conformational ch ange of albumin induced by electrostatic forces within the protein. Di azepam induced a distant accommodation of the protein, an effect accom panied by an enhanced inhibition of the release of protons from albumi n.