Ibuprofen binding to secondary sites allosterically modulates the spectroscopic and catalytic properties of human serum heme-albumin.

The ibuprofen primary binding site FA3-FA4 is located in domain III of human serum albumin (HSA), the secondary clefts FA2 and FA6 being sited in domains I and II. Here, the thermodynamics of ibuprofen binding to recombinant Asp1-Glu382 truncated HSA (tHSA)-heme-Fe(III) and nitrosylated tHSA-heme-Fe(II), encompassing domains I and II only, is reported. Moreover, the allosteric effect of ibuprofen on the kinetics of tHSA-heme-Fe(III)-mediated peroxynitrite isomerization and nitrosylated tHSA-heme-Fe(II) denitrosylation has been investigated. The present data indicate, for the first time, that the allosteric modulation of tHSA-heme and HSA-heme reactivity by ibuprofen depends mainly on drug binding to the FA2 and FA6 secondary sites rather than drug association with the FA3-FA4 primary cleft. Thus, tHSA is a valuable model with which to investigate the allosteric linkage between the heme cleft FA1 and the ligand-binding pockets FA2 and FA6, all located in domains I and II of (t)HSA.