IDENTIFICATION AND CHARACTERIZATION OF AN ECTO(LYSO)PHOSPHATIDIC ACID-PHOSPHATASE IN PAM212 KERATINOCYTES

Intact PAM212 keratinocytes were found to preferentially degrade exoge nous phosphatidic acids (PA) containing short fatty acid chains. The p roduct of this degradation was inorganic phosphate (P-i), suggesting t hat the enzyme was a phosphatase. Systematic studies using enzymatical ly synthesized PA and lysophosphatidic acid (lysoPA) demonstrated that the sn-2 fatty acid chain length was the determining factor for suita bility of PA as substrate for this cell-associated enzyme. Thus 1-acyl -2-lyso-PA provided the best substrate for this enzyme while long-chai n PA were poor substrates. The enzyme was effectively inhibited by NaF and Na3VO4, but was insensitive to inhibitors of alkaline phosphatase or other nonspecific phosphatases. The enzyme activity was solubilize d from intact cells by proteinases, such as trypsin and papain, and th e reaction product P-i was distributed exclusively in the extracellula r medium, suggesting that this (lyso)PA phosphatase is an ectoenzyme. These results unequivocally demonstrated the presence of a (lyso)PA ph osphatase located at the cell surface. This novel ectoenzyme may provi de a mechanism for the inactivation of the potent bioactive phospholip id, lysoPA. (C) 1994 Academic Press, Inc.