| Abstract: | Tonin, a rat enzyme capable of cleaving angiotensinogen, the tetradecapeptide renin substrate and angiotensin I directly to antiotensin II is also shown to cleave beta-lipotropin into beta-LPH 1–50, 1–51, 51–60, 52–60, 61–78 and 79–91, thereby selectively releasing the opiate-like segment beta-LPH 61–78. Its action on ACTH was similar, releasing ACTH 1–8, 1–7, 3–8, 3–7 and 9–39. In both situations the cleavages are of a selective tryptic-chymotryptic type at specific arginine, phenylalanine residues. Comparison of the tonin cleavage with those of trypsin, trypsin in combination with citraconylation of the lysine residues of beta-LPH is made. The data presented show that tonin does not cleave Met-enkephalin and can be used as an enzyme to study the presence of endorphin-like sequences in polypeptides. |
