Long-chain polyunsaturated fatty acids in the sn-2 position of phosphatidylcholine decrease the stability of recombinant high density lipoprotein apolipoprotein A-I and the activation energy of the lecithin:cholesterol acyltransferase reaction.
The lecithin:cholesterol acyltransferase (LCAT) kinetics and activation energy and the stability of apolipoprotein A-I (apoA-I) were investigated using recombinant HDL (rHDL) containing phosphatidylcholine (PC), [3H]cholesterol, and apo A-I. The PC component of the rHDL contained sn-1 16:0 and sn-2 18:1 (POPC), 20:4 (PAPC), 20:5 n-3 (PEPC), or 22:6 n-3 (PDPC) or 10% of the respective PC species and 90% sn-1 18:1, sn-2 16:0 PC ether (OPPC ether). The appVmax of the rHDL containing 100% PC varied 10-fold and was ordered POPC > PEPC > PAPC > PDPC, whereas the appKm values varied 19-43 microns PC. The ether-containing rHDL had appVmax values 17-40% of their respective 100% PC rHDL, but maintained the same rank order. The activation energy of LCAT was lower for rHDL containing long chain polyunsaturated fatty acids (PUFA) compared to rHDL containing 100% POPC or 10% PC/90% OPPC ether. The concentration of guanidine HCl (D1/2) required to denature one-half of the apoA-I on rHDL containing long chain PUFA was reduced (1.2-16 M) compared to those containing 100% POPC or 10% PC/90% OPPC (2.2-2.4 M) and there was a strong correlation (r = 0.71) between LCAT activation energy and the stability of apoA-I (i.e., D1/2). We conclude that long chain PUFA in the sn-2 position of PC decreases the catalytic efficiency of LCAT, the activation energy of the LCAT reaction and the stability of apoA-I on the rHDL particles. The strong association between rHDL apoA-I stability and LCAT activation energy suggests that the temperature-dependent step of the LCAT reaction may be sensitive to the strength of the interaction of apoA-I with rHDL PC.
Parks
J S
JS
Department of Comparative Medicine, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, NC 27157-6279, USA.
Gebre
A K
AK
D016632:Apolipoprotein A-I / Q000737:chemistry*; D002788:Cholesterol Esters / Q000096:biosynthesis; D002942:Circular Dichroism; D004305:Dose-Response Relationship, Drug; D005231:Fatty Acids, Unsaturated / Q000737:chemistry*; D006146:Guanidines / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008075:Lipoproteins, HDL / Q000737:chemistry*; D009994:Osmolar Concentration; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000737:chemistry / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000378:metabolism; D011489:Protein Denaturation; D011994:Recombinant Proteins / Q000737:chemistry
D016632:Apolipoprotein A-I; D002788:Cholesterol Esters; D005231:Fatty Acids, Unsaturated; D006146:Guanidines; D008075:Lipoproteins, HDL; D010713:Phosphatidylcholines; D011994:Recombinant Proteins; D007862:Phosphatidylcholine-Sterol O-Acyltransferase