Prohormone

[1][2] Prohormones can travel the blood stream as a hormone in an inactivated form, ready to be activated later in the cell by post-translational modification.

[4] Often in nature, this cleaving process happens immediately, and a prohormone is quickly converted to a set of one or more peptide hormones.

[6] A commonly consumed example of said precursors are androstenedione and androstenediol, both of which are currently banned substances in the United States.

[10] Prohormones allow for transport and storage of usually-active proteins as inactive peptide chains, though they are much more commonly found in nature as a stable intermediate in the protein-synthesizing process of the cell.

[5] However, other inactive proteins travel in their prohormone form, such as vitamin D, also known as calciferol, which can be produced by the human body via sunlight.

[14] Proamylin, which is cosecreted with proinsulin, requires the above three factors and an amidating monooxygenase to convert itself to an active hormone.

Proinsulin molecule; schematic, topological drawing. B chain (orange), C-peptide (gray), and A chain (green). The C-peptide is seen to bind to the B and A chains and suppress hormonal expression. When cleavage occurs to produce insulin, the B and A chain are connected by disulfide bonds, while the C-peptide is cut out and discarded.