There are seven members of the proprotein convertase (PC) family of secre-ted serine proteases that cleave their substrates at basic amino acids, thereby activating a variety of hormones, growth factors, and viruses. PC1⁄3, PC2 and PC5⁄6A are the only members of the PC family that are targeted to dense core secretory granules, where they carry out the process-ing of proteins that are secreted from the cell in a regulated manner.