Proprotein Convertase 2 (PCSK2) is a subtilisin-like serine peptidase that processes proteins into biologically active products in the secretory pathway. Like other furin/kexin family members, PCSK2 cleaves its substrates primarily after sites of paired basic aa residues (1). Autoactivation of PCSK2 occurs in a post-Golgi compartment of the secretory system (2). Interaction with the secretory protein 7B2 is required for proper activation of PCSK2 (3). The N-terminal domain of 7B2 stabilizes active PCSK2, and a C-terminal fragment of 7B2 can inhibit PCSK2 activity (4). rhPCSK2 was coexpressed with 7B2 to facilitate activation of the enzyme. PCSK2 is a major proteolytic processing enzyme of the regulated secretory pathway of the neuroendocrine system, where it generates a number of hormones and neuropeptides (5). Products of PCSK2 processing include enkephalins, insulin, somatostatin, dynorphin, and LHRH. Within the region used as an immunogen, human PCSK2 shares 97% aa identity with mouse PCSK2.