title: Further characterization of the major forms of reptile beta-endorphin.
abstract: Biosynthetically labeled reptile intermediate pituitary beta-endorphin-sized material was fractionated by SP-Sephadex ion exchange chromatography into two major opiate-active forms which eluted at 0.28 M NaCl and 0.32 M NaCl, respectively; the 0.32 M form of reptile beta-endorphin (mw = 3500), serves as the precursor for the 0.28 M form of reptile beta-endorphin (mw = 3200), (Dores and Surprenant, 1983). Analysis of tryptic digests of these reptile beta-endorphins by paper electrophoresis at pH 3.5 and gel filtration on a Sephadex G-15 column indicated that there are two tyrosine residues, two arginine residues and one methionine residue in reptile beta-endorphin. Furthermore, the NH2-terminal tryptic peptide of both reptile beta-endorphins is approximately nine amino acids in size and contains tyrosine, methionine and arginine. Analyses of chymotryptic/protease digests of the [3H]tyrosine-labeled NH2-terminal tryptic peptide analyzed by descending paper chromatography revealed that the NH2-terminal tyrosine of reptile beta-endorphin is not alpha-N-acetylated. A second tyrosine-containing tryptic peptide was detected in the COOH-terminal region of reptile beta-endorphin; however this tryptic peptide differs in the two forms of reptile beta-endorphin in terms of size and net charge at pH 3.5. These differences account for the apparent molecular weight differences and distinct ion exchange properties of the 0.28 M and 0.32 M forms of reptile beta-endorphin. Thus in the reptile intermediate pituitary the principal post-translational mechanism for modifying beta-endorphin is COOH-terminal proteolytic cleavage.
mesh_terms: D000818:Animals; D002850:Chromatography, Gel; D002918:Chymotrypsin; D004590:Electrophoresis, Paper; D004723:Endorphins / Q000302:isolation & purification*; D007076:Iguanas / Q000502:physiology*; D008116:Lizards / Q000502:physiology*; D008297:Male; D010446:Peptide Fragments / Q000032:analysis; D010902:Pituitary Gland / Q000032:analysis*; D014357:Trypsin; D001615:beta-Endorphin
chemical_list: D004723:Endorphins; D010446:Peptide Fragments; D001615:beta-Endorphin; D002918:Chymotrypsin; D014357:Trypsin