A LYSOPHOSPHOINOSITIDE-SPECIFIC PHOSPHOLIPASE-C DISTINCT FROM OTHER PHOSPHOLIPASE-C FAMILIES IN RAT-BRAIN

Distinct phospholipase C activities capable of hydrolyzing lysophospha tidylinositol (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 activi ty from the membranes, whereas a significant level of lysoPI-PLC activ ity still remained membrane-associated. Most of the lysoPI-PLC activit y was recovered in a 0.5% sodium deoxycholate-0.25 M NaCl extract whic h contained only low levels of PI-PLC activity. Using the separated fr actions, differences between lysoPI-PLC and the known PI-PLC isoforms were examined. A specific peptide inhibitor of PI-PLC, which was previ ously shown to interact with active site regions common to known PI-PL C isoforms, did not suppress the extracted lysoPI-PLC activity. Immuno blot analysis of both the lysoPI-PLC-rich and PI-PLC-rich fractions re vealed that an antiserum against PI-PLC delta 1 cross-reacted with oth er 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-P LC and that lysoPI-PLC possesses a different active site than known PI -PLC isoforms. (C) 1995 Academic Press, Inc.