Identification of a β-endorphin-like peptide in cultured human placental cells

Abstract

In the pituitary, adrenocorticotropic hormone (ACTH)- and β-endorphin-related peptides are post-translationally derived from a common precursor glycoprotein^1,2. ACTH- and β-endorphin-like peptides have been demonstrated in human placental extracts by radioimmunoassay (RIA), bioassay and opioid radioreceptor assay^3–7. Recently, we have shown that short-term cultured human placental trophoblastic cells synthesize a high molecular weight glycoprotein(s) physicochemically similar to the pituitary common precursor molecule; ACTH(9–15)- and β-endorphin(1–9)-like fragments were detected in a tryptic digest of this precursor. Pulse-chase experiments revealed that radiolabel disappeared from the molecule and accumulated in smaller molecular species having either ACTH or β-endorphin antigenic determinants⁸. We now report the use of re verse-phase HPLC to resolve the tryptic fragments of one component of β-endorphin-like peptide synthesized in placental cells, and show that it is comparable to synthetic human β-endorphin. The two reverse-phase HPLC systems used resolved all tryptic fragments of human β-endorphin (β_h-endorphin) with differing selectivities, thus providing two unique ‘fingerprints’, in analogy to conventional two-dimensional peptide analysis. The fact that identical maps were obtained for β_h-endorphin and the placental peptide in both systems, provides strong evidence that they are structurally identical.