Secretory PAF-acetylhydrolase of the rat hepatobiliary system: characterization and partial purification.
Hepatocytes and Kupffer cells in primary culture both secrete plasma-type platelet-activating factor-acetylhydrolase (pPAF-AH) into serum-free culture medium. The rate of secretion of pPAF-AH by Kupffer cells was 20 to 25 times higher than from hepatocytes, and Kupffer cells expressed a higher level of pPAF-AH mRNA than did hepatocytes. Purified liver cell-secreted pPAF-AH exhibited a major protein band of 65-67 kDa on SDS-PAGE; this was the band predominantly labeled when the enzyme catalytic center was reacted with [3H]diisopropylfluorophosphate ([3H]DFP). Rat bile collected from cannulated bile ducts contained significant PAF-AH activity, and bile samples possessed a prominent band at 30-32 kDa, which was the exclusive target for [3H]DFP. Experiments using tunicamycin, an inhibitor of N-linked glycosylation, and endoglycosidase H suggested that pPAF-AH secreted constitutively by cultured hepatocytes and Kupffer cells is glycosylated. The present study supports the notion that hepatic secretion of pPAF-AH into the blood contributes to the regulation of PAF and oxidized phospholipid levels in the circulation, whereas secretion of PAF-AH into the bile may allow hepatic control of these phospholipid signaling molecules in the gastrointestinal tract.
Svetlov
S I
SI
Department of Biochemistry, University of Texas Health Science Center at San Antonio 78284-7760, USA.
Howard
K M
KM
Debuysere
M S
MS
Olson
M S
MS
D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D000818:Animals; D001646:Bile / Q000378:metabolism*; D002478:Cells, Cultured; D055598:Chemical Phenomena; D002621:Chemistry; D007728:Kupffer Cells / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D010741:Phospholipases A / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats
D012333:RNA, Messenger; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase