title: Location and characterization of the suramin binding sites of human serum albumin.
abstract: The objective of the present study was to investigate the location of the high-affinity suramin binding sites on the human serum albumin molecule. For this purpose, circular dichroism and equilibrium dialysis experiments were performed on the interaction between suramin and a large peptic and a large tryptic fragment of albumin, the former comprising domains one and two of the albumin structure and the latter domains two and three. The equilibrium dialysis experiments revealed that albumin and the fragments have a comparable total affinity for suramin. Furthermore, all three proteins display a similar pH dependence of the unbound fraction of suramin. The circular dichroism experiments revealed that only the suramin-albumin and the suramin-peptic fragment complexes can undergo the pH dependent neutral-to-base or N-B conformational change, whereas the suramin-tryptic fragment complex lacks this ability. It is likely that the main parts of the high-affinity binding sites for suramin are located in domain two of the albumin molecule. The nature of these binding sites is discussed. The deprotonation of histidine and other positively charged residues taking part in salt bridges between suramin and albumin is, in all probability, the main cause of the decrease in affinity of suramin for albumin as the pH is raised from 6 to 9.
authors.affiliation: Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Utrecht, The Netherlands.
authors.forename: O J
authors.initials: OJ
authors.lastname: Bos
authors.forename: E L
authors.initials: EL
authors.lastname: Vansterkenburg
authors.forename: J P
authors.initials: JP
authors.lastname: Boon
authors.forename: M J
authors.initials: MJ
authors.lastname: Fischer
authors.forename: J
authors.initials: J
authors.lastname: Wilting
authors.forename: L H
authors.initials: LH
authors.lastname: Janssen
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D003956:Dialysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008433:Mathematics; D011487:Protein Conformation; D012709:Serum Albumin / Q000032:analysis*; D013498:Suramin / Q000032:analysis*; D014357:Trypsin
chemical_list: D012709:Serum Albumin; D013498:Suramin; D014357:Trypsin