Processing of the Common Precursor to ACTH and Endorphin in Mouse Pituitary Tumor Cells and Monolayer Cultures from Mouse Anterior Pituitary
Adrenocorticotropin (ACTH) and β-lipotropin (β-LPH) have been shown to be derived from the same high-molecular-weight precursor protein (common precursor) in mouse pituitary tumor cells (AtT-20/D16v cells) (Mains et al., 1977; Nakanishi et al., 1977; Roberts and Herbert, 1977a, b). When messenger RNA from AtT-20 cells is translated in a reticulocyte cell-free system, a single form of the precursor is synthesized with a molecular weight of 28,500 (28.5K pro-ACTH-endorphin) (Roberts and Herbert, 1977a,b). The use of the “polysome runoff technique” (Dintzis, 1961) has made it possible to arrange the tryptic peptides of ACTH and β-LPH relative to one another (Roberts and Herbert, 1977b) in the 28.5K precursor as shown in the model of structure in Fig. 1. In this model, β-LPH is located at the C terminus of the precursor and ACTH is adjacent to β-LPH near the middle of the molecule, leaving an unidentified sequence of approximately 100 amino acids at the N terminus. A 31,000-molecular-weight form of the precursor has been isolated from AtT-20 cells and shown to have a structure very similar to that depicted in Fig. 1 (Eipper and Mains, 1978). Thus, a single protein contains the sequence of α(l–39)ACTH, α-melanocyte-stimulating hormone (α-MSH), and the component hormones of β-LPH: β-endorphin, β-MSH, and Met-enkephalin.
KeywordsAnterior Pituitary Tryptic Peptide Common Precursor Precursor Form Radioactive Amino Acid
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