HUMAN PLACENTAL IMMUNOREACTIVE CORTICOTROPIN, LIPOTROPIN, AND BETA-ENDORPHIN - EVIDENCE FOR A COMMON PRECURSOR

The concentrations and molecular sizes of immunoreactive 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 wt of tissue, respectively. A partially purified extract applied to a Sephadex G-50 column contained high MW 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 [SDS] had ACTH, LPH and .beta.END immunoreactivities, indicating that there was a component or components containing antigenic determinants for all of these peptides. SDS/polyacrylamide gel electrophoresis of the affinity-purified placental extract revealed at least 2 high MW components (MW .apprxeq. 48,000 and 36,000) with all 3 immunoreactivities. The placenta may synthesize ACTH, LPH and .beta.END from a common precursor molecule.