PROOF OF ALKALINE PHOSPHODIESTERASE-I AS A PHOSPHATIDYLINOSITOL-ANCHOR ENZYME

1. Ectoenzyme release from kidney brush border membranes of Rattus nor vegicus and Sus scrofa domesticus by phosphatidylinositol-specific pho spholipase C (PIPLC) of Bacillus thuringiensis was studied. 2. The lev els of specific activities of ectoenzymes in R. norvegicus kidney brus h border membranes were higher than those in S. scrofa domesticus. Abo ut 10-fold higher values were found for specific activities of alkalin e phosphatase and gamma-glutamyl transpeptidase in R. norvegicus. 3. A lkaline phosphodiesterase I, alkaline phosphatase and 5'-nucleotidase were released from both R. norvegicus and S. scrofa domesticus brush b order membranes, while gamma-glutamyl transpeptidase and dipeptidyl pe ptidase IV were not solubilized. The enzyme release by the action of P IPLC was suppressed when purified anti-PIPLC antibody was added to the reaction mixture. This suggests that enzyme release must be due to th e direct action of PIPLC on kidney brush border membranes. 4. The rele ased alkaline phosphodiesterase I from kidney of S. scrofa domesticus had a molecular weight of 240,000 and was activated by Mg2+ and Ca2+, but strongly inhibited by EDTA.