Calorimetric indication of the molten globule-like state of cytochrome c induced by n-alkyl sulfates at low concentrations

• Published in: The Journal of chemical thermodynamics Vol. 35; no. 2; pp. 199 - 207
• Main Authors: Chamani, J, Moosavi-Movahedi, A.A, Saboury, A.A, Gharanfoli, M, Hakimelahi, G.H
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-02-2003; Elsevier
• Subjects: Anionic surfactant; Biological and medical sciences; Compaction; Conformational dynamics in molecular biology; Cytochrome c; Fundamental and applied biological sciences. Psychology; ITC indication; Molecular biophysics; Molten globule; Cytochrome c; Anionic surfactant; Compaction; ITC indication; Molten globule; Medium effect; Denaturation; Calorimetry; Thermal analysis; Acid medium; Cytochrome e
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/S0021-9614(02)00312-9

The molten globule state has been proposed as a major intermediate of protein folding. However it has proven difficult to obtain thermodynamic data characterizing this state. To explore an alternative approach for characterization of the molten globule state,
n-alkyl sulfates induced formation of the molten globule state of horse cytochrome
c at pH 2 was studied by isothermal titration calorimetry (ITC). Titration of the acid unfolded state of cytochrome
c with sodium octyl sulfate, sodium dodecyl sulfate or sodium tetradecyl sulfate, generated an exothermic reaction for formation of the molten globule state. The effects of various
n-alkyl sulfates on the acid unfolded state of cytochrome
c demonstrated that the increased alkyl chain length enhanced the exothermic values of calorimetric enthalpy and induced a more compact molten globule states. The heat contents agreed well with the conformational transition measured by molar ellipticity at 222
nm ([
θ]
222) and Stoke radius (
Rs) values. These results emphasize that isothermal titration calorimetry provides a reasonable alternative method for characterization of the molten globule state.