263-270Mammalian
alkaline phosphatase (ALP) is attached to the plasma membrane by a unique
glycosylphosphatidylinositol (GPI) anchor. The influence of such a complex
anchoring device on the enzyme function is not fully understood. Here,
we report the effect of cleavage of the GPI anchor on the activity of goat
liver plasma membrane ALP (GLPM-ALP). Phosphatidylinositol-specific
phospholipase C (PI-PLC) purified from Bacillus
cereus was used for the cleavage of the GPI anchor (delipidation) and hence
for release of ALP from the membrane. Detergents — octyl-β-D-glucopyranoside
(OG) and triton X100 (TX100) were also used for solubilization of ALP from the
membrane. Resistance to solubilization by TX100 suggested the association of
GPI-ALP with lipid rafts. Solubilization of GLPM-ALP with OG had no effect on
the enzyme activity; however, delipidation with PI-PLC resulted in enhanced ALP
activity. Kinetic analysis showed catalytic activation of PI-PLC-treated
GLPM-ALP with an increase in Vmax
(35%) without a significant change in Km.
Moreover, this change in Vmax
was observed to be independent of pH and buffer. The results suggested the
implication of GPI anchor in modulating the catalytic property of GLPM-ALP,
thus indicating the role of this special anchoring structure in the enzyme
regulation