Abstract
Levels of alkaline phosphatase (ALP) activity in the incisor pulps of rats, mice and hamsters are about ten times greater than those of rabbits, bovines, or pigs. When ALP was extracted from rat dental pulps and analyzed by polyacrylamide gel electrophoresis with Nonidet P-40 (native-PAGE) or sodium dodecyl sulfate (SDS-PAGE) under a non-reducing condition, the enzyme was divided into ALP-N1 and ALP-N2 on native-PAGE, or into 130k and 155k on SDS-PAGE. ALP-N1 and -N2 corresponded to 130 and 155k on two dimensional-PAGE, respectively. ALP-N1 (130k) changed to ALP-N2 (155k) after simply incubating the ALP extract at 37°C. It has been proven that the transformation of ALP is not caused by ALP-binding proteins, but is specifically caused by glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) in the ALP extract sample.
In this study, the purified ALP-N1 had the same pI (4.3) and binding affinity for ALP-N2 antibody as the purified ALP-N2. However, fatty acids (C14-C18) were detected only in the purified ALP-N1 by gas chromatography, and not in the purified ALP-N2 or ALP-N1 treated with phosphatidylinositol-specific phospholipase C. The level of SDS that combined with ALP-N1 was significantly more than that which combined with ALP-N2 without fatty acids. These findings suggest that the ALP-N1 (130k) moved faster than the ALP-N2 (155k) on SDS-polyacrylamide gel.
This study demonstrated that ALP in rat dental pulps is a homo-dimer composed of 77 k-subunits, and that two ALP-forms, with and without fatty acids, are produced by GPI-PLD in blood during the process of extracting ALP from the tissue.
