NITROXIDE REDUCTION WITH ASCORBIC-ACID IN SPIN-LABELED HUMAN PLASMA LDL AND VLDL

The LDL and VLDL were spin labeled with Tempo which partitions both in the aqueous and lipid phase. The ESR spectra were measured in the equ ilibrium state as well as during the reduction of the spin label with ascorbic acid. The kinetics of the concentration decay curves was para metrized with two exponentials. The theoretical simulation of the expe rimental spectra revealed a drastic linewidth narrowing in the VLDL sa mples exposed to the ascorbic acid. Since the transport properties of the specific monolayer are reflected in the observed reaction rates, t he analysis of the fatty acid composition of phospholipids, triglyceri des and cholesterol esters in LDL and VLDL was performed. It is conclu ded that different lipid packing al the surface of LDL and VLDL might be the consequence of different intermolecular forces between phosphol ipids and cholesterol. This finding was connected to the experimentall y detected different reaction kinetics in LDL and VLDL as well as thei r different susceptibility to the ESR linebroadening effects during th e nonequilibrium conditions of the spin label reduction with ascorbic acid. Copyright (C) 1997 Elsevier Science Ireland Ltd.