REDUCED BETA-STRAND CONTENT IN APOPROTEIN B-100 IN SMALLER AND DENSERLOW-DENSITY-LIPOPROTEIN SUBCLASSES AS PROBED BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY

The secondary structure of apolipoprotein B-100 in low-density lipopro tein (LDL) subfractions was analysed by Fourier-transform IR spectrosc opy. LDLs were isolated in three density ranges by gradient centrifuga tion of human plasma from healthy volunteers. The spectra revealed dif ferences in the lipid content and composition of the three LDL fractio ns. The secondary structure of apolipoprotein B-100 was the same in th e two fractions corresponding to the large less-dense LDL particles, w hereas a lower content of beta-strands was found in the third fraction corresponding to the smaller denser LDL particles. Analysis of the sp ectroscopic data suggests that, in the same set of LDL subfractions, t he particle size is probably the cause of the observed differences in apolipoprotein B-100 secondary structure.