Human placental immunoreactive corticotropin, lipotropin, and beta-endorphin: evidence for a common precursor

The concentrations and molecular sizes of immunoreactive corticotropin (ACTH), lipotropin (LPH, beta LPH plus gamma LPH), gamma LPH, and beta-endorphin (beta END) were determined in human placental extracts. Serial dilutions of a water extract of placenta generated competitive binding curves parallel with that of the standard in each assay. The concentrations of ACTH, LPH, gamma LPH, and beta END were 3.3, 0.8, 0.7, and 1.1 ng/g wet weight of tissue, respectively. A partially purified extract applied to a Sephadex G-50 column contained high Mr components with ACTH, LPH, gamma LPH, and beta END immunoreactivities. The extract was applied to an immune affinity chromatography column consisting of affinity-purified (1-24)ACTH antiserum covalently bound to agarose. The material that adsorbed to the column and eluted with buffer containing sodium dodecyl sulfate had ACTH, LPH, and beta END immunoreactivities, indicating that there was a component or components containing antigenic determinants for all of these peptides. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of the affinity-purified placental extract revealed at least two high Mr components (Mr approximately 48,000 and 36,000) with all three immunoreactivities. These data suggest, but do not prove, that the placenta synthesizes ACTH, the LPHs, and beta END from a common precursor molecule.