Corticotropin and β-endorphin-like materials are native to unicellular organisms

Abstract

Multiple molecular forms of immunoreactive corticotropin (ACTH) and β-endorphin were present in extracts of a unicellular eukaryote (Tetrahymena pyriformis). One form of immunoreactive ACTH reacted similarly with two different ACTH antisera (one specific for the 11-24 sequence and the other with determinants within sequences 1-14 and 17-39) and migrated with synthetic hACTH-(1-39) in a gel filtration system. This form also exhibited ACTH bioactivity in a dispersed rat adrenal cell bioassay system, with a mean immunoassay/bioassay ratio of 1.5. Gel filtration revealed multiple size classes of immunoreactive β-endorphin; a major peak of radioreceptor activity was detected which exhibited a K_av similar to that of authentic β-endorphin. A major portion of immunoreactive β-endorphin-sized material exhibited retention times similar to those of synthetic human and camel β-endorphin upon reverse-phase high-pressure liquid chromatography. These distinctive properties and specificities would seem to exclude the presence of limited homologies with sequences present in other proteins. High molecular weight material containing both ACTH and β-endorphin antigenic determinants was also demonstrated, suggesting, but not proving, the presence of a common precursor molecule.