Alkaline phosphatase isoforms in bile and serum and their generation from cells in vitro.

Alkaline phosphatase is anchored to cell membranes by a glycosyl-phosphatidylinositol anchor and is present in bile and plasma in various isoforms. The formation of these isoforms depends upon mechanisms of release and subsequent complex formation. Evidence is presented for an enzymatic activity possibly a glycosyl-phosphatidylinositol-specific phospholipase D (GPI-PLD), in serum that releases an isoform incapable of further complex formation, whereas such an activity is absent from bile.