How are protein hormones made from prohormones?

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Hormone Many important physiological functions of vertebrates are controlled by steroid hormones.

Protein hormones are synthesized through a multi-step process within endocrine cells. After messenger ribonucleic acid (mRNA) directs the synthesis of a relatively inert precursor known as a prohormone at the endoplasmic reticulum, the prohormone is transported to the Golgi apparatus.1

Within the Golgi apparatus, the prohormone is packaged into vesicles called secretory granules. As these granules migrate toward the cell surface, a proteolytic enzyme cleaves the prohormone, separating its inactive region from the active hormone. Finally, the active hormone is discharged into the extracellular fluid through a process called exocytosis.1