TY - JOUR
T1 - Both tissue and serum phospholipases release rat intestinal alkaline phosphatase
AU - Eliakim, R.
AU - Becich, M. J.
AU - Green, K.
AU - Alpers, D. H.
PY - 1990
Y1 - 1990
N2 - Rat intestinal alkaline phosphatase (IAP) is unique among the brush-border membrane enzymes in that it is released bidirectionally (lumen and blood) and exists in either soluble (serum) or particulate (cellular) form. To elucidate the mechanism of membrane release, we examined the effects of phosphatidylinositol-specific phospholipase C (PtdIns-PLC) and serum anchor-specific phospholipase D( PLD) on the solubility of the various tissue forms of IAP. The 'solubility' of cytosol IAP could be explained in part by intracellular PtdIns-PLC activity, detected by production of acidic IAP isomers, and by ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-sensitive PtdIns hydrolysis. Contamination with serum (abundant with anchor-specific PLD) was responsible for the complete or partial solubilization of IAP that was found during processing of light mucosal scrapings. Anchor-specific PLD activity was increased after fat feeding, and the IAP released did not react with antiserum that recognizes the PtdIns-PLC-released phospholipid portion of trypanosomal variable surface glycoprotein. These data are consistent with the hypothesis that, after secretion from the enterocyte bound to a phospholipid-rich membranous particle, IAP release into serum is mediated by serum anchor-specific PLD. The soluble forms of IAP in the lumen and the cytosol fraction appear to be due to a combination of endogenous PtdIns-PLC activity and anchor-specific PLD contamination that occurs during cell fractionation.
AB - Rat intestinal alkaline phosphatase (IAP) is unique among the brush-border membrane enzymes in that it is released bidirectionally (lumen and blood) and exists in either soluble (serum) or particulate (cellular) form. To elucidate the mechanism of membrane release, we examined the effects of phosphatidylinositol-specific phospholipase C (PtdIns-PLC) and serum anchor-specific phospholipase D( PLD) on the solubility of the various tissue forms of IAP. The 'solubility' of cytosol IAP could be explained in part by intracellular PtdIns-PLC activity, detected by production of acidic IAP isomers, and by ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-sensitive PtdIns hydrolysis. Contamination with serum (abundant with anchor-specific PLD) was responsible for the complete or partial solubilization of IAP that was found during processing of light mucosal scrapings. Anchor-specific PLD activity was increased after fat feeding, and the IAP released did not react with antiserum that recognizes the PtdIns-PLC-released phospholipid portion of trypanosomal variable surface glycoprotein. These data are consistent with the hypothesis that, after secretion from the enterocyte bound to a phospholipid-rich membranous particle, IAP release into serum is mediated by serum anchor-specific PLD. The soluble forms of IAP in the lumen and the cytosol fraction appear to be due to a combination of endogenous PtdIns-PLC activity and anchor-specific PLD contamination that occurs during cell fractionation.
KW - brush-border membrane
KW - phosphatidylinositol
KW - phospholipase C
KW - phospholipase D
UR - http://www.scopus.com/inward/record.url?scp=0025169302&partnerID=8YFLogxK
U2 - 10.1152/ajpgi.1990.259.4.g618
DO - 10.1152/ajpgi.1990.259.4.g618
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AN - SCOPUS:0025169302
SN - 0193-1857
VL - 259
SP - G618-G625
JO - American Journal of Physiology - Gastrointestinal and Liver Physiology
JF - American Journal of Physiology - Gastrointestinal and Liver Physiology
IS - 4 22-4
ER -