A phospholipase D specific for the phosphatidylinositol anchor of cell-surface proteins is abundant in plasma.
An enzyme activity capable of degrading the glycosyl-phosphatidylinositol membrane anchor of cell-surface proteins has previously been reported in a number of mammalian tissues. The experiments reported here demonstrate that this anchor-degrading activity is also abundant in mammalian plasma. The activity was inhibited by EGTA or 1,10-phenanthroline. It was capable of removing the anchor from alkaline phosphatase, 5'-nucleotidase, and variant surface glycoprotein but had little or not activity toward phosphatidylinositol or phosphatidylcholine. Phosphatidic acid was the only 3H-labeled product when this enzyme hydrolyzed [3H]myristate-labeled variant surface glycoprotein. It could be distinguished from the Ca2+-dependent inositol phospholipid-specific phospholipase C activity in several rat tissues on the basis of its molecular size and its sensitivity to 1,10-phenanthroline. The data therefore suggest that this activity is due to a phospholipase D with specificity for glycosyl-phosphatidylinositol structures. Although the precise physiological function of this anchor-specific phospholipase D remains to be determined, these findings indicate that it could play an important role in regulating the expression and release of cell-surface proteins in vivo.
Oklahoma Medical Research Foundation, Oklahoma City 73104.
M G
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Prasad
D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D002850:Chromatography, Gel; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D008563:Membrane Lipids / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D010712:Phosphatidic Acids / Q000096:biosynthesis; D010716:Phosphatidylinositols / Q000378:metabolism*; D010739:Phospholipase D / Q000097:blood* / Q000378:metabolism; D010740:Phospholipases / Q000097:blood*; D010743:Phospholipids / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D013379:Substrate Specificity
D006023:Glycoproteins; D008563:Membrane Lipids; D008565:Membrane Proteins; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; D010743:Phospholipids; D010740:Phospholipases; D000469:Alkaline Phosphatase; D010739:Phospholipase D