Partial amino acid sequence of human placental lactogen precursor and its mature hormone form produced by membrane-associated enzyme activity

The precursor form of human placental lactogen, synthesized by a wheat germ extract cell-free system, has been partially sequenced and found to contain a high percentage of leucine residues within its first 20 amino acids. The partial NH₂-terminal structure appears to be: {A figure is presented} The precursor form of hPL, produced by an ascites extract cell-free system, was cleaved by a membrane-associated enzyme into a form which exhibits the methionine and valine residues in NH₂-terminal positions identical to those of native human placental lactogen.