RAT BETA‐LPH, GAMMA‐LPH AND BETA‐ENDORPHIN BIOSYNTHESIZED BY ISOLATED CELLS OF PARS INTERMEDIA AND PARS DISTALIS

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Abstract
Rat pars intermedia cells were incubated for 3 h with the following amino acids: 35S-Met and 3H-Phe; 3H-Val; and 3H-Val and 3H-Lys. Radioactive .gamma.-lipotropin, .beta.-lipotropin and .beta.-endorphin were purified on carboxymethyl-cellulose and characterized by polyacrylamide disc gel electrophoresis at pH 4.5, MW estimation and microsequencing. Rat .gamma.-lipotropin differed slightly from ovine .gamma.-lipotropin in its NH2-terminal amino acid sequence, in containing no Met and having Phe at position 6, Val at positions 13 and 27, and Lys at position 20. The same variations were observed in the sequence of rat .beta.-lipotropin, while rat .beta.-endorphin was indentical to the ovine .beta.-endorphin. Following a 3 h pulse of rats pars distalis, the cells were extracted with care to avoid .beta.-lipotropin degradation by proteolytic enzymes. A peptide was purified and identified to be rat .beta.-endorphin; .beta.-endorphin is biosynthesized in pars distalis and is not an extraction artifact.