NAPSA, also known as Napsin-A, belongs to the peptidase A1 family and may be involved in processing of pneumocyte surfactant precursors. The activation peptides of aspartic proteinases plays role as inhibitors of the active site. These peptide segments, or pro-parts, are deemed important for correct folding, targeting, and control of the activation of aspartic proteinase zymogens. The pronapsin A is predicted to be a fully functional, glycosylated aspartic proteinase precursor containing an RGD motif and an additional 18 residues at its C-terminus. Recombinant human NAPSA, fused to His-tag at N-terminus, was expressed in E.coli and purified by conventional chromatography.