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Unfolding of dimeric creatine kinase in urea and guanidine hydrochloride as measured using small angle X‐ray scattering with synchrotron radiation
Author(s) -
Zhou Jun-Mei,
Fan Ying-Xin,
Kihara Hiroshi,
Kimura Kazumoto,
Amemiya Yoshiyuki
Publication year - 1997
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(97)01120-4
Subject(s) - guanidine , hydrochloride , denaturation (fissile materials) , chemistry , radius of gyration , urea , crystallography , molecule , dissociation (chemistry) , small angle x ray scattering , circular dichroism , scattering , nuclear chemistry , organic chemistry , polymer , physics , optics
The denaturation of dimeric creatine kinase (CK) induced by urea and guanidine hydrochloride (GuHCl) has been studied by small angle X‐ray scattering (SAXS), which is a direct way to measure the changes in the overall dimensions of a protein molecule. The radii of gyration ( R g ) of CK are 29±0.4 Å in the native state and 46±1.5 Å in the unfolded state in either 8 M urea or 3 M GuHCl. The transition curves of urea denaturation derived from the R g values and the zero angle intensity ( I (0)) are similar to that from intrinsic fluorescence, indicating that the changes in the molecular shape, the tertiary structure and the dissociation of the subunits proceed simultaneously. In the case of GuHCl‐induced denaturation, the dramatic increases both in R g and in I (0) in 0.3–0.5 M GuHCl suggest clearly that soluble aggregates form at low GuHCl concentrations. The aggregates dissociate and the molecule unfolds at higher GuHCl concentrations. The results suggest that the mechanisms of CK denaturation in urea and in GuHCl are somewhat different and the intermediate in GuHCl denaturation can much more easily form soluble aggregates.