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Proprotein convertase 1(PC1), also called "prohormone convertase 1", is an enzyme that performs the proteolytic cleavage of prohormones to their intermediate (or sometimes completely cleaved) forms. It is present only in neuroendocrine cells such as brain, pituitary and adrenal, and most often cleaves after a pair of basic residues within prohormones but can occasionally cleave after a single arginine. It binds to a protein known as proSAAS, which also represents its endogenous inhibitor. PC1 is synthesized as a 99kDa proform quickly converted to an 87 kDa major active form, which itself is nearly completely cleaved to a 66 kDa active form within neuroendocrine cells.
Proprotein convertase 1 is the enzyme largely responsible for the synthesis of insulin. Another prohormone convertase, proprotein convertase 2 plays a more minor role in insulin biosynthesis, but a greater role in glucagon biosynthesis. The knockout of this enzyme is not lethal in mice or humans, most likely due to the presence of the second convertase.
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