JBC, Vol. 252, Issue 24, 8778-8780, Dec, 1977
Conformational relaxations of urea- and guanidine hydrochloride-unfolded ferricytochrome c
T. Y. Tsong
Several recent studies of protein the unfolded proteins. In urea- and
guanidine HCl-unfolded ferricytochrome c (horse heart), an acid-induced
spin state transformation of the heme group has been detected by the heme
absorptions, Trp-59 fluorescence, and the intrinsic viscosity of protein.
Kinetics of this second conformational transition, by the temperature jump
and stopped flow methods, are complex. One rapid reaction (tau1),
pH-independent, occurs in a 50-mus range; the second reaction (tau2), in a
1-ms range, depends linearly upon pH and is faster at the alkaline side; a
third reaction (tau3), in a 1-s range, shows a sigmoidal transition at pH
5.1 and is faster at the acidic side. The results are consistent with a
kinetic scheme which involves protein conformational changes in the
transformation of the heme coordination state. The kinetics, along with
previous equilibrium studies, indicate that ligand or charge interactions
within a protein molecule are not completely prohibited even in strongly
denaturing conditions, such as in high concentrations of urea and guanidine
HCl. Thus, local structures of peptide chain associated with these
interactions can exist in the unfolded protein.
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