The Free Energy of Dissociation of Oligomeric Structure in Phycocyanin Is Not Linear with Denaturant
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- 作者：Katie L. Thoren ; Katelyn B. Connell ; Taylor E. Robinson ; David D. Shellhamer ; Margaret S. Tammaro ; Yvonne M. Gindt
- 刊名：Biochemistry
- 出版年：2006
- 出版时间：October 3, 2006
- 年：2006
- 卷：45
- 期：39
- 页码：12050 - 12059
- 全文大小：120K
- 年卷期：v.45,no.39(October 3, 2006)
- ISSN：1520-4995
文摘
Using SEC HPLC and fluorescence anisotropy, absorption spectra were assigned to the specificoligomeric structures found with phycocyanin. The absorption spectra were used to quantify the populationof each oligomeric form of the protein as a function of both urea concentration and temperature.Phycocyanin hexamers dissociate to trimers with equilibrium constants of 10-6 to 10-5. Phycocyanintrimers dissociate to monomers with equilibrium constants of 10-15 to 10-12. Both dissociation constantsincrease linearly with increasing urea concentration, and 
G
values calculated from the equilibriumconstants fit best with an exponential function. Our findings appear in contrast with the commonly usedlinear extrapolation model, Gurea = Gwater + A[denaturant], in which a linear relationship exists betweenthe free energy of protein unfolding or loss of quaternary structure and the denaturant concentration. Ourdata examines a smaller range of denaturant concentration than generally used, which might partiallyexplain the inconsistency.
G values calculated from the equilibriumconstants fit best with an exponential function. Our findings appear in contrast with the commonly usedlinear extrapolation model, Gurea = Gwater + A[denaturant], in which a linear relationship exists betweenthe free energy of protein unfolding or loss of quaternary structure and the denaturant concentration. Ourdata examines a smaller range of denaturant concentration than generally used, which might partiallyexplain the inconsistency.