An active site peptide from human placental alkaline phosphatase

A preparation of human placental alkaline phosphatase was labelled covalently at the active site with [32P]orthophosphate. Treatment with trypsin gave essentially one radioactive peptide, the active site peptide, of approximately 2300 molecular weight. Dansylation of the peptide showed that the amino-terminal residue was glycine. After acid hydrolysis the only radioactively-labelled amino acid present was serine phosphate. The amino acid composition was similar to those compositions reported for active site peptides from other alkaline phosphatases.