IDENTIFICATION OF A NOVEL HUMAN PHOSPHATIDIC-ACID PHOSPHATASE TYPE-2 ISOFORM

Tno human isoforms of membrane associated phosphatidic acid phosphatas e have been described (PAP-2a and -2b), and both enzymes have been sho wn to have broad substrate specificity and wide tissue distribution [K ai et al., J. Biol. Chem. 272 (1997) 24572-24578]. With this report we describe a third isoform, PAP-2c, that we found by searching the data base of expressed sequence tags (dbEST) with PAP-2a and PAP-2b sequenc es, Key structural features described previously in PAP-2a and -2b, in cluding the glycosylation site, putative transmembrane domains, and th e proposed catalytic site, are conserved in the novel phosphatase. The kinetics of the three enzymes were compared using as substrates phosp hatidic acid, lysophosphatidic acid, and N-oleoyl ethanolamine phospha tidic acid, K-m values for each of the substrates, respectively, were (in mu M) PAP-2a: 98, 170, 116; PAP-2b: 100, 110, 56; and PAP-2c: 150, 340, 135, Expression of PAP-2c mRNA is more restricted than the two p reviously described isoforms. (C) 1998 Federation of European Biochemi cal Societies.