小腸ALPの基質特異性とその役割

抄録

The phosphohydrolytic activity in human liver, bone, term placenta and intestinal alkaline phosphatases (ALPs) determined with phosphorylcholine (PC), phosphorylethanolamine, pyridoxal-5'-phosphate and p-nitrophenylphosphate at pH 8.8 was studied. In this process, the differences in their enzymatic natures as apparent K_m, V_max/K_m, transphosphorylation activity, amino acid inhibition and susceptibility to Na₂HPO₄ were evaluated. The apparent K_m value (0.9mM) of the intestinal ALP with PC showed the highest of all ALPs tested. Although intestinal ALP hydrolysed PC the most, the affinity order of choline as a transphosphorylation acceptor was liver/bone>intestinal>>placental ALP(s). In addition, the intestinal ALP activity with PC was most susceptible to Na₂HPO₄ in the tested ALP. Furthermore, the intestinal ALP activity and phospholipid contents in the rat serum were well accorded to one another. Consequently, present results suggest that the intestinal ALP may regulate a metabolism of choline/PC as part of phosphatidylcholine and/or phosphatidylcholine dependent synthesis of triglyceride.