Si. Svetlov et al., SECRETORY PAF-ACETYLHYDROLASE OF THE RAT HEPATOBILIARY SYSTEM - CHARACTERIZATION AND PARTIAL-PURIFICATION, American journal of physiology: Gastrointestinal and liver physiology, 37(5), 1998, pp. 891-900
Hepatocytes and Kupffer cells in primary culture both secrete plasma-t
ype platelet-activating factor-acetylhydrolase (pPAF-AH) into serum-fr
ee culture medium. The rate of secretion of pPAF-AH by Kupffer cells w
as 20 to 25 times higher than from hepatocytes, and Kupffer cells expr
essed a higher level of pPAF-AH mRNA than did hepatocytes. Purified li
ver 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 c
atalytic center was reacted with [H-3]diisopropylfluorophosphate ([H-3
]DFP). Rat bile collected from cannulated bile ducts contained signifi
cant PAF-AH activity, and bile samples possessed a prominent band at 3
0-32 kDa, which was the exclusive target for [H-3]DFP. Experiments usi
ng tunicamycin, an inhibitor of N-linked glycosylation, and endoglycos
idase H suggested that pPAF-AH secreted constitutively by cultured hep
atocytes and Kupffer cells is glycosylated. The present study supports
the notion that hepatic secretion of pPAF-AH into the blood contribut
es to the regulation of PAF and oxidized phospholipid levels in the ci
rculation, whereas secretion of PAF-AH into the bile may allow hepatic
control of these phospholipid signaling molecules in the gastrointest
inal tract.