THE SUBDOMAIN STRUCTURE OF HUMAN SERUM-ALBUMIN IN SOLUTION UNDER DIFFERENT PH CONDITIONS STUDIED BY SMALL-ANGLE X-RAY-SCATTERING

Small-angle X-ray scattering (SAXS) was used to study structural chara cteristics of human serum albumin (HSA) in solution under different pH conditions. Guinier analysis of SAXS results yielded values of the mo lecular radius of gyration ranging from 26.7 Angstrom to 34.5 Angstrom for pH varying from 2.5 to 7.0. This suggests the existence of signif icant differences in the overall shape of the molecule at different pH . Molecular models based on subdomains with different spatial configur ations were proposed. The distance distribution functions associated w ith these models were calculated and compared with those determined fr om the experimental SAXS intensity functions. The conclusion of this S AXS study is that the arrangement of molecular subdomains is clearly p H dependent; the molecule adopting more or less compact configuration for different pH conditions. The conclusions of this systematic study on the modification in molecular shape of HSA as a response to pH chan ges is consistent with those of previous investigations performed for particular pH conditions.