Preliminary characterization of in vitro synthesized hypothalamic precursor ACTH/beta-endorphin-like material.

We have previously shown that cultured bovine pituitary or hypothalamic cells incorporate 3H-labeled amino acids into high molecular weight glycoproteins containing the antigenic determinants of both corticotropin (ACTH) and beta-endorphin. We now report resolution of this 3H-labeled ACTH/beta-endorphin-like material into two predominant size classes upon SDS polyacrylamide-gel electrophoresis with apparent molecular weights (Mr) of 41 500 +/- 1600 and 36 000 +/- 1100. Isoelectric focusing revealed these components to be basic proteins with apparent isoelectric points greater than 8.5. Overnight trypsinization generated a 3H-labeled fragment comigrating with synthetic beta-lipotropin (61-69) [beta-endorphin (1-9)] upon paper electrophoresis which was immunoprecipitable with antibody directed against the corresponding synthetic fragment. Limited trypsinization of bovine immunoreactive ACTH/beta-endorphin extracted from freshly obtained bovine hypothalamic and anterior pituitary tissue, generated fragments which possessed ACTH bioreactivity. Both bovine pituitary and hypothalamic derived material are similar with respect to these foregoing physiochemical parameters and appear to be larger than the reported forms in mouse pituitary.