Endonuclease, PolyU Specific (ENDOU)

Placental protein-11 was initially identified as a protein associated with normal human placenta and with various malignant neoplasms of breast, ovary, testis, and stomach. The cDNA encodes a 42-kD soluble protein of 369 amino acids, including an N-terminal hydrophobic region of 18 amino acids typical of secretory proteins.

PP11 protein expressed in E. coli displayed diisopropyl fluorophosphate (DPF)-inhibitable amidolytic activity, suggesting function as a serine protease, although categorization of the protein as an esterase could not be ruled out. Western blot also revealed an inactive 45-kD precursor protein in PP11-transformed E. coli.