Conformation of human serum high density lipoprotein and its peptide components

CIRCULAR dichroic (CD)¹ and optical rotatory dispersion (ORD)² measurements indicate that the protein moiety of human serum high density lipoproteins (HDL) contains a relatively high content of α-helical conformation. The low density lipoprotein fraction (LDL), on the other hand, has been found by CD and infrared spectroscopy to be relatively less helical in conformation and to contain considerable pleated sheet or β-structure^3-6. The CD spectrum of HDL exhibits negative troughs at 222 and 208 nm, characteristic of α-helical conformation, while that of LDL has a major trough at 215-218 nm, suggestive of β-structure, and a shoulder at 208 to 210 nm compatible with some helical and/or random structure⁸ (Table 1).