Rat beta-LPH, gamma-LPH and beta-endorphin biosynthesized by isolated cells of pars intermedia and pars distalis. Further characterization.

Rat pars intermedia cells were incubated for 3 h with the following amino acids: (a) 35S-methionine and 3H-phenylalanine, (b) 3H-valine; and (c) 3H-valine and 3H-lysine. Radioactive gamma-lipotropin, beta-lipotropin and beta-endorphin were purified on carboxymethyl-cellulose and characterized by polyacrylamide disc gel electrophoresis at pH 4.5, molecular weight estimation and micro-sequencing. Rat gamma-lipotropin was shown to differ slightly from ovine gamma-lipotropin in its NH2-terminal amino acid sequence, in containing no methionine and having phenylalanine at position 6, valine at positions 13 and 27, and lysine at position 20. The same variations were observed in the sequence of rat beta-lipotropin, while rat beta-endorphin was shown to be identical to the ovine beta-endorphin. Following a 3-h pulse of rat 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, thus demonstrating that beta-endorphin is biosynthesized in pars distalis and is not an extraction artifact.