CHROMAFFIN GRANULE ASPARTIC PROTEINASE PROCESSES RECOMBINANT PROOPIOMELANOCORTIN (POMC)

Our search for proteases responsible for proenkephalin (PE) processing in adrenal medulla led to the isolation of a 70 kDa aspartic proteina se that cleaves PE between the basic residues of the Lys-Arg processin g site (1). Studies in pituitary have also identified a similar aspart ic proteinase that processes POMC (2,3). To compare the chromaffin gra nule (CG) 70 kDa aspartic proteinase with that in pituitary, processin g of recombinant POMC by the CG enzyme was examined. POMC was expresse d in the T7 expression system in E. coli, and purified to homogeneity. The CG 70 kDa aspartic proteinase converted POMC to 27 and 22 kDa ban ds that were detected by anti-N-POMC immunoblots, and to 26, 22, and 1 4 kDa bands that were immunoreactive with anti-beta-lipotropin. POMC p roducts represented by these bands indicate appropriate POMC processin g by the CG 70 kDa aspartic proteinase. These results, combined with t he similar biochemical properties of these two enzymes, suggest that t he CG 70 kDa aspartic proteinase resembles the POMC-converting enzyme (PCE), an aspartic proteinase in pituitary (2,3). (C) 1995 Academic Pr ess, Inc.