Isoforms of apolipoprotein A-II in human plasma and thoracic duct lymph. Identification of proapolipoprotein A-II and sialic acid-containing isoforms.
Proapolipoprotein (apo-) A-II and several isoforms of apo-A-II including sialylated isoforms were identified in human plasma and thoracic duct lymph. Proapo-A-II secreted by HepG2 cells was identified by a combination of immunoblots and [14C]arginine incorporation. Proapo-A-II which contains 2 arginine residues could be readily differentiated from mature apo-A-II which contains no arginine. The pI of proapo-A-II is 6.79, whereas the pI of the major apo-A-II isoform in plasma and lymph is 4.90. Minor apo-A-II isoforms have pI values of 5.17, 4.68, 4.42, and 4.20, respectively. Sialoisoforms of apo-A-II were identified, which had a higher apparent molecular weight on sodium dodecyl sulfate-gel electrophoresis than the major isoform and disappeared following neuraminidase treatment. The relative quantity of proapo-A-II was relatively constant in lymph very low density lipoproteins, lymph high density lipoproteins, and plasma high density lipoproteins, whereas the sialoforms and the other minor isoforms of apo-A-II were greater in lymph very low density lipoproteins and the lowest in plasma high density lipoproteins.
Lackner
K J
KJ
Edge
S B
SB
Gregg
R E
RE
Hoeg
J M
JM
Brewer
H B
HB
D016633:Apolipoprotein A-II; D001054:Apolipoproteins A / Q000032:analysis*; D006528:Carcinoma, Hepatocellular / Q000032:analysis; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007525:Isoelectric Focusing; D007536:Isomerism; D008075:Lipoproteins, HDL / Q000032:analysis*; D008113:Liver Neoplasms / Q000032:analysis; D008196:Lymph / Q000032:analysis*; D009439:Neuraminidase / Q000378:metabolism; D011498:Protein Precursors / Q000032:analysis*; D012794:Sialic Acids / Q000032:analysis*
D016633:Apolipoprotein A-II; D001054:Apolipoproteins A; D008075:Lipoproteins, HDL; D011498:Protein Precursors; D012794:Sialic Acids; D009439:Neuraminidase