Distribution of apolipoprotein A-IV among lipoprotein subclasses in rat serum.
The distribution of apolipoproteins (apo) A-I, A-IV, and E in sera of fed and fasted rats was studied using various methods for the isolation of lipoproteins. Serum concentrations of apoA-I and apoA-IV decreased significantly during fasting (16 and 31%, respectively), while apoE concentrations remained essentially the same. Chromatography of sera on 6% agarose columns showed that apoA-IV is present on HDL and as so-called "free" apoA-IV. The concentration of "free" apoA-IV decreased six- to seven-fold during fasting, explaining the decrease in total serum apoA-IV. Serum apoA-I and apoE are almost exclusively associated with HDL-sized particles. When sera are centrifuged at a density of 1.21 g/ml, marked quantities of apoA-I (8-9%) and apoE (11-22%) are recovered in the "lipoprotein-deficient" infranatant, suggesting that ultracentrifugation affects the integrity of serum HDL. The nature of the chromatographically separated carriers of serum apoA-IV was investigated by quantitative immunoprecipitation. From these studies, it is concluded that apoA-IV in rat serum is present in at least three fractions: 1) particles with the size and composition of HDL, containing both apoA-I and apoA-IV and possibly minor quantities of apoE; 2) HDL-sized particles containing apoA-IV, but no apoA-I or apoE; 3) "free" apoA-IV probably containing small amounts of bound cholesterol and phospholipid.
D000818:Animals; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000097:blood*; D001057:Apolipoproteins E / Q000097:blood; D002784:Cholesterol / Q000097:blood; D005215:Fasting; D007158:Immunologic Techniques; D008074:Lipoproteins / Q000097:blood* / Q000302:isolation & purification; D008075:Lipoproteins, HDL / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D014461:Ultracentrifugation
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D001057:Apolipoproteins E; D008074:Lipoproteins; D008075:Lipoproteins, HDL; C022205:apolipoprotein A-IV; D002784:Cholesterol