Insulin
Structure, Sythesis & Transport
- A peptide hormone made of 51 amino acids
- Formed of 2 chains (α and β) connected by disulphide bridges
- Synthesised as proinsulin with chains joined by C-peptide
- C-peptide excised by endopeptidases in the endoplasmic reticulum of β cells prior to release
- C-peptide is 31 amino acid sequence has no known biological function
- Can be used as marker of endogenous insulin secretion
- Stored in secretory granules and is secreted by the cells via exocytosis
- It enters the portal system with half cleared by first pass through the liver
- Circulates entirely in an unbound form