FIGURE 7.

Identification of Lys⁸⁵² as an essential residue for the expression of activity. A, alignment of the last 12 amino acids of NPP1 and NPP2. The bold underlined sequence indicates the amino acids that are conserved between both proteins. Using a deletion-insertion strategy, the last 12 amino acids of NPP2 were exchanged for those of NPP1, yielding NPP2-(C1). Equal amounts of WT NPP2 and NPP2-(C1) were estimated by immunoblotting with c-Myc antibodies. The same volumes were used to study the lysophospholipase-D activity (n = 3, mean ± S.E.). B, the residues of the LKT-triad were mutated as indicated, and the corresponding mutants in the medium (subset) were assayed for their lysophospholipase-D (LPase D) activities. The results are represented as means (n = 3) ± S.E.