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Cooperative thermal transitions of bovine and human apo‐α‐lactalbumins: evidence for a new intermediate state
Author(s) -
Veprintsev Dmitry B,
Permyakov Serge E,
Permyakov Eugene A,
Rogov Vladimir V,
Cawthern Kevin M,
Berliner Lawrence J
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)00841-7
Subject(s) - molten globule , chemistry , circular dichroism , isothermal microcalorimetry , intermediate state , crystallography , fluorescence , analytical chemistry (journal) , thermodynamics , chromatography , enthalpy , philosophy , physics , theology , quantum mechanics
The thermal denaturation of bovine and human apo‐α‐lactalbumins at neutral pH has been studied by intrinsic protein fluorescence, circular dichroism (CD), and differential scanning microcalorimetry (DSC) methods. Apo‐α‐lactalbumin possesses a thermal transition with a midpoint about 25–30°C under these conditions (pH 8.1, 10 mM borate, 1 mM EGTA), which is reflected in changes in both fluorescence emission maximum and quantum yield. However, the CD showed a decrease in ellipticity at 270 nm with a midpoint at about 10–15°C, while DSC shows the transition within the region of 15–20°C. The non‐coincidence of transition monitored by different methods suggests the existence of an intermediate state in the course of the thermal denaturation process. This intermediate state is not the classical molten globule state which occurs at higher temperature (i.e. denatured state at these conditions) [D.A. Dolgikh, R.I. Gilmanshin, E.V. Brazhnikov, V.E. Bychkova, G.V. Semisotnov, S.Y. Venyaminov and O.B. Ptitsyn, FEBS Letters , 136 (1981) 311–315] and has physical properties intermediate between the native and molten globule states.