<unk> s 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. Proinsulin, for example, is seen in nature as a brief precursor to insulin, as it is produced on the ribosomes of the cell, transported to the Golgi apparatus as proinsulin, then is converted to insulin immediately after reaching the Golgi apparatus. It is also primarily stored as insulin. However, other inactive proteins travel in their<unk>  form, such as vitamin D, also known as calciferol, which can be produced by the human body via sunlight. The main regulator of<unk>  to hormone conversion is<unk>  convertase. Located in the Golgi apparatus, it uses endoproteolytic cleavage to separate peptide hormones from each other and removes extended amino acid residues that hinder the inactive peptides from being active proteins. Because of this role,<unk>  convertase is one of the deciding factors for regulation of hormone content in the body, as it has the ability to change an inactive protein with unsubstantial hormonal effect on the body, to a fully active protein with a meaningful hormonal effect. For peptide hormones, the conversion process from<unk>  to hormone (pro-protein to protein) typically occurs after being exported to the endoplasmic reticulum and often requires multiple processing enzymes. Proamylin, which is cosecreted with proinsulin, requires the above three factors and an amidating monooxygenase to convert itself to an active hormone. Some pro-protein precursors, such as preproinsulin, also go through this process, with the added step of removing a signal peptide by signal peptidases, to convert said precursors into<unk> s.
Prohormone
Xenohormone
Neurohormone
Hormone
Local hormone
Gastrointestinal hormone
Sex hormone
Neuropeptide