Abstract
Apolipoprotein A-I, the major structural polypeptide of human high-density lipoproteins, activates lecithin: cholesterol acyltransferase, the cholesterol ester-forming enzyme in plasma. Apolipoprotein A-I, like several other apolipoproteins, exhibits structural adapatability, which is manifest in a low free energy of stabilization and facile changes in secondary structure. We have investigated the dual effects of guanidinium chloride (GdmCl) and pressure perturbation at low GdmCl concentrations on apolipoprotein A-I conformational states, using fluorescence detection. Pressure alone (up to 3 kilobar) is insufficient to fully denature apolipoprotein A-I, and results in formation of metastable state(s). However, in conjunction with low concentrations of GdmCl the calculated volume change upon pressure denaturation increases from approx. - 50 ml/mol to -90 ml/mol. The free energy of denaturation by pressure perturbation ranges from 1.4 to 1.8 kcal/mol, but the conformational states induced by pressure and GdmCl perturbation are most likely different. The physico-chemical properties of native and pressure-denatured conformational states can be, readily and reversibly, measured by fluorescence techniques. Biological activity of apolipoprotein A-I in the form of lecithin:cholesterol acyltransferase activation, is also reversible upon pressure perturbation. Samples of apolipoprotein A-I exposed to 2 kbar for an hour activated lecithin: cholesterol acyltransferase equally well as controls. To delineate more precisely the conformational states of apolipoprotein A-I under pressure, time-dependent anisotropy decay measurements, capable of resolving rotational heterogeneity, will be required.
Original language | English (US) |
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Pages (from-to) | 215-221 |
Number of pages | 7 |
Journal | Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism |
Volume | 836 |
Issue number | 2 |
DOIs | |
State | Published - Sep 11 1985 |
Keywords
- (Human HDL)
- Apolipoprotein A-I
- cholesterol acyltransferase
- Guanidinium chloride
- Hydrostatic pressure
- Lecithin
- Protein denaturation
ASJC Scopus subject areas
- Endocrinology
- Biophysics
- Biochemistry