Structure of two adrenal polypeptides containing multiple enkephalin sequences

Two enkephalin-containing polypeptides of 4000 and 5000 daltons have been isolated from extracts of bovine adrenal medulla. Each polypeptide was purified to homogeneity and subjected to sequence analysis. The entire primary structure of the 4000-dalton polypeptide was established by a combination of automated Edman degradation and chemical analysis of its tryptic peptides. The polypeptide contains two copies of the [Met]-enkephalin sequence, one at the amino terminus and the other at the carboxyl terminus. Chemical analysis of the tryptic peptides and automated Edman degradation of the 5000-dalton polypeptide indicated the presence of a [Leu]enkephalin sequence at the carboxyl terminus and an internal [Met]enkephalin sequence. Both of the above enkephalin-containing polypeptides appear to be intermediates in the biosynthesis of the enkephalins.