Thermodynamics of apocytochrome b5 unfolding

Open Access
Publisher Website
Google Scholar
Abstract
Apocytochrome b5 from rabbit liver was studied by scanning calorimetry, limited proteolysis, circular dichroism, second derivative spectroscopy, and size exclusion chromatography. The protein is able to undergo a reversible two-state thermal transition. However, transition temperature, denaturational enthalpy, and heat capacity change are reduced compared with the holoprotein. Apocytochrome b5 stability in terms of Gibbs energy change at protein unfolding (ΔG) amounts to ΔG = 7 ± 1 kJ/mol at 25 °C (pH 7.4) compared with ΔG = 25 kJ/mol for the holoprotein. Apocytochrome b5 is a compact, nativelike protein. According to the spectral data, the cooperative structure is mainly based in the core region formed by residues 1–35 and 79–90. This finding is in full agreement with NMR data (Moore, C.D. & Lecomte, J.T.J., 1993, Biochemistry 32, 199–207).