prothorm

Prothorm is a term sometimes used to describe a precursor form of a hormone that requires enzymatic processing to become active. In many contexts, prothorm is synonymous with prohormone, though the latter term is far more widely used in contemporary biology and medicine. Prothorms are typically synthesized as larger, biologically inactive polypeptides in secretory cells and stored in secretory vesicles until they are cleaved by proteases to release one or more active hormones, and sometimes additional peptide fragments.

Activation of a prothorm usually involves endoproteolytic cleavage at specific sites, such as dibasic residues, by processing enzymes like subtilisin-like convertases (for example PC1/3 and PC2) or other proteases. The resulting mature hormone can be a single peptide or a set of active fragments derived from the same precursor gene. This maturation mechanism allows a single prohormone to yield multiple signaling molecules, contributing to hormonal diversity while conserving genetic and cellular resources.

Examples commonly cited in physiology include proinsulin, which is cleaved to generate insulin and C-peptide, and proglucagon, which yields glucagon and other peptides. Prohormone-based maturation is a fundamental concept in endocrinology, reflecting how organisms regulate hormone activity through controlled proteolysis rather than producing only fully active peptides directly.

Clinical relevance arises when processing steps are defective or dysregulated, leading to imbalanced hormone levels or altered biomarker patterns. Prohormone measurements can aid in diagnosing and understanding disorders of hormone production and secretion. See also prohormone, propeptide, and proteolytic processing.