Acid-ethanol extracts of fetal bovine pancreas were examined for the presence of β-endorphin-like immunoreactivity. Gel-filtration analyses revealed the presence of a major large-molecular-weight β-endorphin immunoreactive species of ∼20K∆. This molecular form maintained its size upon resubmission to gel filtration in the presence of 6 M guanidine hydrochloride, separated from the bulk of the glucagon immunoreactivity upon ion-exchange chromatography, showed proportional dilution in the β-endorphin radioimmunoassay, and interacted in a biospecific manner with Concana-valin-A-Sepharose.

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