Biochi~ica et Biophysica Acta. 1126 (19921 05-1 t3

High density iipoprotcins (HDL) consist of a mixture of chemically and functionally distinct families of particles defined by their characteristic apolipoprotcin (Apo) cotnposition. The two major lipoprotcin families are lipopro~ein A-! (LP-A-I) and lipoprotein A-! : A-It (LP-A-I: A-It). This study describes the isolation of a third minor HDL family of particles referred to as lipoprotcin A-[I (LP-A-II) because it lacks APOA-! and contains ApoA-l | as its main or sole apolipoprotein constituent. Because ApoA-II is an integral protein constituent of three distinct [ipoprotcin families (LP-A-I:A-I!, LP-A-II:B:C: D:E and LP-A-ll), LP-A-I! particles wore isolated from whole plasma by sequential immunoaffinity chromatography on immunosorbcrs with amisera to APOA-ll, APOB and APOA-I, respectively. In normolipidemic sul~ects, the concentration f LP-A-II particles, based on APOA-ii c~ntent, is4-18 mg/dl accounting for 5-20 % of the total ApoA-il not associatcd with ApoB-containing lipopmteins. The lipid composition of LP-A-II particles [s characterized bylow percentages of trigiycerides and cholesterol ester:, and a high p~rcentagc of phospholipids in compari.~on with lipid composition of LP-A-I and LP-A-! : A.lt. The major part of LP-A-II particles contain APOA-II a ~ the sole apoiipoprotein constituent; however, small subsets of LP.A.II particles may also contain APOD and other minor apolipoprotcins. The I;.pid/protein ratio of LP-A-!I is higher than those of LP-A-I and LP-A-I:A-II. In homo~ygou