title: Contribution of alpha helix formation in human plasma apolipoproteins to their enthalpy of association with phospholipids.
abstract: The human plasma apolipoproteins, apo-A-II and apo-C-III, assocaite with phospholipid with a concurrent increase in alpha helical structure of the apoprotein and an exothermic enthalpy of association. A linear correlation of the increase in alpha helical structure and the exothermic enthalpy of association gave a value of -1.3 kcal/mol of amino acid residues converted from a random coil to an alpha helical structure. This value is very close to that of alpha helix formation by charged polyamino acids (-1.2 kcal/mol) and suggests that amino acid side chains contribute little or no heat to the random coil leads to alpha helix transition in the plasma apolipoproteins. In the absence of a change in alpha helix in the apolipoproteins studied here, the enthalpy of association is practically nil, suggesting that alpha helix formation is a major enthalpic contribution to the total free energy of lipid-apolipoprotein association.
mesh_terms: D001053:Apolipoproteins / Q000097:blood; D002942:Circular Dichroism; D006801:Humans; D008075:Lipoproteins, HDL / Q000097:blood; D008079:Lipoproteins, VLDL / Q000097:blood; D010743:Phospholipids / Q000097:blood; D011485:Protein Binding; D011487:Protein Conformation; D013816:Thermodynamics
chemical_list: D001053:Apolipoproteins; D008075:Lipoproteins, HDL; D008079:Lipoproteins, VLDL; D010743:Phospholipids