[1]Peptide hormone biosynthesis is the cellular production and molecular maturation of peptides that act as hormonal signals. Translation generates precursor proteins that enter the secretory pathway and undergo processing to produce mature peptide products. Proprotein convertases catalyze specific cleavage reactions within these precursors, frequently at sites containing basic amino-acid residues [2]. The intracellular localization of a processing enzyme positions its catalytic activity within the appropriate secretory compartment [3]. Recognition of paired basic residues is a molecular feature of several precursor-processing reactions and contributes to the selection of cleavage sites . Compartmental pH and calcium conditions can further regulate the activity of processing enzymes, as in proinsulin conversion [4]. Precursor sequence, protease specificity, and secretory-compartment chemistry together organize the formation and maturation of the hormonal peptide [5].