Proprotein Convertases in Health and Disease

Secretory proteins, such as hormones, enzymes, and receptors, constitute a broad group of biochemically active molecules that are essential for cellular function. Post-translational processing of their precursor molecules, which occurs through endoproteolytic cleavage, results in the formation of biologically active secretory proteins at the intended target sites and represents an evolutionary mechanism through which complex species maintain homeostasis, nimbly responding to internal and external challenges. At least five classes of proteolytic enzymes have been identified, encompassing more than 66,000 protein sequences classified into 50 clans and 184 families in accordance with their catalytic mechanisms and evolutionary lineages.

Proprotein Convertases in Health and Disease
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Interesting basic science article in the New England Journal looking at one way that organisms regulate the presence and quantity of active compounds in cells.  Note that this is one example of epigenetic cell regulation,