A Lysophosphoinositide-Specific Phospholipase C Distinct from Other Phospholipase C Families in Rat Brain

Distinct phospholipase C activities capable of hydrolyzing lysophosphatidylinositol (lysoPI-PLC) or phosphatidylinositol (PI-PLC) have been demonstrated in rat brain membranes. Treatment of brain membranes with 1 M NaCl or 1% sodium cholate solubilized a majority of PI-PLC activity from the membranes, whereas a significant level of lysoPI-PLC activity still remained membrane-associated. Most of the lysoPI-PLC activity was recovered in a 0.5% sodium deoxycholate-0.25 M NaCl extract which contained only low levels of PI-PLC activity. Using the separated fractions, differences between lysoPI-PLC and the known PI-PLC isoforms were examined. A specific peptide inhibitor of PI-PLC, which was previously shown to interact with active site regions common to known PI-PLC isoforms, did not suppress the extracted lysoPI-PLC activity. Immunoblot analysis of both the lysoPI-PLC-rich and PI-PLC-rich fractions revealed that an antiserum against PI-PLCδ1 cross-reacted with other PI-PLC isoforms, but not significantly with lysoPI-PLC. Furthermore, lysoPI-PLC was more resistant to sulfhydryl reagents than was PI-PLC. Our results indicate that lysoPI-PLC is an enzyme distinct from PI-PLC and that lysoPI-PLC possesses a different active site than known PI-PLC isoforms.