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Phosphorylcholine as a unique substrate for human intestinal alkaline phosphatase
T Irino1, M Matsushita, Y Sakagishi
1Department of Clinical Chemistry, Saitama College of Health, Japan.
The International Journal of Biochemistry
|February 1, 1994
Summary
Human intestinal alkaline phosphatase (ALP) uniquely hydrolyzes phosphorylcholine (PC), showing higher affinity for choline. This suggests PC may play a role in choline metabolism, particularly within phosphatidylcholine pathways.
Area of Science:
- Biochemistry
- Enzymology
- Human Physiology
Background:
- Alkaline phosphatases (ALPs) are crucial enzymes with diverse physiological roles.
- Understanding the substrate specificity of different ALP isoenzymes is key to elucidating their functions.
- Phosphorylcholine (PC) is a component of cell membranes and has implications in various metabolic processes.
Purpose of the Study:
- To investigate the enzymatic characteristics of human liver, bone, placental, and intestinal ALPs.
- To determine the substrate preference and kinetic properties of these ALPs using various phosphate-containing compounds.
- To specifically assess the interaction of human intestinal ALP with phosphorylcholine (PC).
Main Methods:
- Enzyme kinetics assays were performed on purified human liver, bone, placental, and intestinal ALPs.
- Substrates included phosphorylcholine (PC), phosphorylethanolamine, pyridoxal-5'-phosphate, and p-nitrophenylphosphate.
- Enzyme activity was measured at a weakly alkaline pH, and kinetic parameters like apparent Km were determined.
Main Results:
- Human intestinal ALP exhibited the highest apparent Km value for PC among all tested ALPs.
- Intestinal ALP demonstrated the highest hydrolysis rate for PC and a greater affinity for choline as a transphosphorylating acceptor.
- Intestinal ALP activity with PC was uniquely sensitive to inhibition by Na2HPO4 compared to other ALPs.
Conclusions:
- Phosphorylcholine (PC) serves as a unique substrate for human intestinal alkaline phosphatase.
- The distinct enzymatic properties suggest a specific role for intestinal ALP in PC or choline metabolism.
- Findings may link intestinal ALP activity to the metabolism of PC within phosphatidylcholine.