PHOSPHORYLCHOLINE AS A UNIQUE SUBSTRATE FOR HUMAN INTESTINAL ALKALINE-PHOSPHATASE

1. The enzymatic nature of human liver, bone, placental and intestinal alkaline phosphatases (ALPs) were investigated with phosphorylcholine (PC), phosphorylethanolamine, pyridoxal-5'-phosphate and p-nitropheny lphosphate at a weakly alkaline pH. 2. The apparent K-m value of intes tinal ALP with PC was the highest of all ALPs tested. Intestinal ALP h ydrolyzes PC the most and has higher affinity for choline as a transph orsphorylating acceptor than the other ALPs. In addition, the intestin al ALP activity with PC was most susceptible to Na2HPO4, in the tested ALPs. 3. The present results suggested that PC is a unique substrate for human intestinal ALP, which may be related to the metabolism of PC or choline as part of phosphatidylcholine.