Two peptidases that convert 125 I-Lys-Arg(Met)enkephalin and 125 I-(Met)enkephalin-Arg6 , respectively, to 125 I-(Met)enkephalin in bovine adrenal medullary chromaffin granules

Abstract

Two peptidases which convert ¹²⁵I‐Lys‐Arg‐ME and ¹²⁵I‐ME‐Arg⁶, respectively, to ¹²⁵I‐ME, have been identified and characterized in bovine adrenomedullary chromaffin granules. The former is referred to as a secretory granule peptidase (SGP) and the latter as a carboxypeptidase B‐like enzyme (CPB‐like) [7] which is here further characterized. SGP cleaved ¹²⁵I‐Lys‐Arg‐ME to produce only ¹²⁵I‐ME and was localized in chromaffin granules which contained co ^{2 +}‐stimulated CPB‐like activity, ME, and catecholamines. Both the SGP and the CPB‐like enzymes appear to be thiol‐metalloproteases. While the CPB‐like enzyme seems likely to be involved in processing the enkephalin precursors [7], SGP may function as a trypsin‐like or aminopeptidase enzyme in secretory granules.