Figure 3.

Effect of oxidation by Cu²⁺ on the apparent transition temperatures in HDL. Numbers correspond to oxidation stages in Fig. 1. HDL (2.5 mg/mL protein in buffer B), which were oxidized to various stages by incubation with CuSO₄, were used for DSC experiments (D) or were diluted to 33 μg/ml by buffer B containing 150 mM NaCl for CD experiments (A–C); the samples were heated at a constant rate of 11 °C/h (A–C) or 90 °C/h (D). The CD (A) and 90° light scattering data (B) were recorded simultaneously at 222 nm during heating and cooling from 25–98 °C; the data are shifted along Y-axis to avoid overlap. The heating curves in panels B, C show two consecutive transitions that involve protein unfolding/dissociation and HDL fusion followed by HDL rupture.³⁷ Negative slopes in the light scattering melting curves in C may result from an optical artifact and from the temperature dependence of the refractive index.

(C) Temperature of HDL fusion as a function of oxidation degree determined from the melting data in panels A, B.

(D) Heat capacity C_p(T) of HDL that were non-oxidized (nHDL), mildly oxidized (stage 2, mHDL), or extensively oxidized (stage 7, oxHDL) were recorded by DSC during heating at 90 °C/h. The data are shifted along the Y-axis to avoid overlap; HDL fusion and rupture transitions are indicated.