Demonstration that the enzyme that converts precursor of apolipoprotein A-I to apolipoprotein A-I is secreted by the hepatocarcinoma cell line Hep G2.
The conversion of the precursor of apolipoprotein A-I (proapoA-I) to apolipoprotein A-I (apoA-I) is known to occur extracellularly by an enzyme that has been shown to be present in plasma. The hepatocarcinoma-derived cell line Hep G2, when grown in culture, secretes proapoA-I. We now show that this cell line also secretes the converting enzyme that correctly processes proapoA-I to mature apoA-I as determined by radio-sequence analyses. The secreted enzyme is inhibited by EDTA and 1,10-phenanthroline, is activated by Ca2+ and is unaffected by both phenylmethylsulfonyl fluoride and diisoprophylfluorophosphate in the same way as the converting enzyme previously described in the plasma. The conversion of proapoA-I to apoA-I effected by this enzyme obeys first-order kinetics and is linear over the first 4 h with a calculated initial velocity of 3.3% conversion per hour. The converting activity is secreted in a time-dependent fashion and parallels the mass of total secreted protein.
Edelstein
C
C
Department of Medicine, Pritzker School of Medicine, University of Chicago, Illinois 60637.
Kaiser
M
M
Piras
G
G
Scanu
A M
AM
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000096:biosynthesis* / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology*; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007700:Kinetics; D008113:Liver Neoplasms / Q000201:enzymology*; D011498:Protein Precursors / Q000378:metabolism*
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D011498:Protein Precursors