Biosynthesis of beta-endorphin, beta-lipotropin and the putative ACTH-LPH precursor in the frog pars intermedia.

When frog pars intermedia are incubated for 3 h with radioactive methionine, the predominant labeled peptide is one with an apparent molecular weight of 33, 100. This peptide can be immunoprecipitated with antisera against β-melanotropin (β-MSH), adrenocorticotrophin (ACTH), and β-endorphin and is believed to be the common precursor of ACTH and β-lipotropin (β-LPH). Immunoprecipitation experiments have also demonstrated the presence of labeled β-LPH and β-endorphin. The labeled β-endorphin has been shown to behave identically to sheep β-endorphin on both carboxymethyl-cellulose chromatography and polyacrylamide gel electrophoresis. Frog β-endorphin has methionine as the fifth residue, as do all other β-endorphins that have been sequenced.