Case Studies

Notable Peptide Examples

Well-studied peptides that illustrate the diversity of structure and function in biology and medicine.

GLP-1 receptor agonists underpin modern metabolic and weight-loss drugs.

Insulin

A 51-amino-acid peptide hormone produced by pancreatic beta cells. It was the first peptide therapeutic and revolutionized diabetes treatment. Structurally it consists of two chains (A and B) linked by disulfide bonds.

51 amino acids

Primary role: Metabolic regulation (glucose uptake)

Key note: 1921 (Banting & Best)

Oxytocin

A 9-amino-acid neuropeptide and hormone synthesized in the hypothalamus. Famous for roles in uterine contraction during childbirth, milk ejection, and social bonding behaviors.

9 amino acids

Primary role: Neuroendocrine & social signaling

Key note: 1953 (du Vigneaud, Nobel Prize)

GLP-1 (Glucagon-like peptide-1)

An incretin hormone (30-31 aa) released from intestinal L-cells after meals. It potentiates insulin secretion, suppresses glucagon, and slows gastric emptying. Basis for blockbuster drugs like semaglutide.

30-31 amino acids

Primary role: Glucose homeostasis & appetite

Key note: 1980s

Substance P

An 11-amino-acid neuropeptide of the tachykinin family. Primary neurotransmitter for pain signals (nociception) from peripheral nerves to the spinal cord; also involved in inflammation and vomiting.

11 amino acids

Primary role: Pain transmission & inflammation

Key note: 1931 (von Euler & Gaddum)

Defensins

A large family of cationic antimicrobial peptides (typically 30-50 aa) produced by neutrophils and epithelial cells. They kill microbes by membrane disruption and also modulate immune responses.

30-50 amino acids

Primary role: Innate immunity & host defense

Key note: 1980s (human) / earlier in insects

B-type Natriuretic Peptide (BNP)

A 32-amino-acid cardiac hormone released by ventricular myocytes in response to stretch. Promotes natriuresis, diuresis, and vasodilation. Widely used as a biomarker (NT-proBNP) for heart failure diagnosis.

32 amino acids (active form)

Primary role: Cardiovascular volume regulation

Key note: 1988

Endorphins (β-endorphin)

Endogenous opioid peptides (31 aa for β-endorphin) produced in the pituitary and brain. They bind μ-opioid receptors to produce analgesia, euphoria, and stress relief.

31 amino acids (β-endorphin)

Primary role: Pain relief & reward

Key note: 1970s

Cyclosporin A

A cyclic 11-amino-acid peptide produced by fungi. Famous as a potent immunosuppressant that revolutionized organ transplantation by inhibiting calcineurin and T-cell activation.

11 amino acids (cyclic)

Primary role: Immunosuppression

Key note: 1970s (Sandoz)

Note

These examples represent only a tiny fraction of known peptides. Many more (including thousands of synthetic analogs) are being studied for therapeutic potential. Structure-activity relationship (SAR) studies and chemical modifications are central to turning natural peptides into drugs.