1. What Are Peptides? A Fundamental Overview

Peptides are short chains of amino acids linked by peptide bonds, covalent bonds formed through a dehydration reaction between the carboxyl group (-COOH) of one amino acid and the amino group (-NH₂) of another.

Based on chain length, peptides are generally classified as:

• Dipeptides: composed of 2 amino acids
• Oligopeptides: typically 3–20 amino acids
• Polypeptides: usually 20–50 amino acids
• Proteins: more than 50 amino acids with complex three-dimensional structures

Compared to proteins, peptides typically have lower molecular weight (commonly <10 kDa) and simpler structures, often lacking fully stable tertiary conformations.

2. Structural Characteristics of Peptides

Similar to proteins, peptides may exhibit hierarchical structural organization:

• Primary structure: linear amino acid sequence
• Secondary structure: localized folding such as α-helices and β-sheets
• Tertiary structure: observed in longer peptides, though generally less stable than proteins

This structural flexibility contributes to their high specificity and bioactivity.

3. Biological Functions of Peptides

Peptides play diverse roles in biological systems, functioning as:

Signaling Molecules and Hormones

• Insulin (51 amino acids): regulates glucose metabolism
• Oxytocin (nonapeptide): involved in social bonding and childbirth

Neurotransmitters and Modulators

• Endorphins: natural analgesic peptides
• Substance P: involved in pain transmission

Antimicrobial Agents

• Defensins: disrupt microbial cell membranes

Enzymes and Precursors

• Many enzymes are synthesized as inactive peptide precursors (zymogens)

Structural Components

• Peptide fragments derived from collagen contribute to tissue strength

4. Applications Across Industries

(1) Pharmaceutical Sector

Peptides have emerged as a promising class of therapeutics due to their high specificity and relatively low toxicity.

• GLP-1 receptor agonists such as Liraglutide are widely used in diabetes management
• Peptide-based anticancer agents are being developed for targeted therapy

However, challenges remain, including enzymatic degradation and limited oral bioavailability, often requiring chemical modification or advanced delivery systems.

(2) Cosmetics and Skincare

Peptides are widely used in functional skincare formulations:

• Signal peptides: stimulate collagen synthesis (e.g., Matrixyl)
• Carrier peptides: facilitate trace element transport (e.g., copper peptides)

These properties make peptides key active ingredients in anti-aging and repair-focused products.

(3) Nutrition and Functional Foods

Bioactive peptides derived from soy or milk proteins have demonstrated:

• Antihypertensive effects
• Antioxidant properties

(4) Research and Biotechnology Tools

• Antigen peptides for antibody production
• Cell-penetrating peptides (e.g., TAT peptide) for intracellular delivery

5. Peptide Manufacturing Technologies

Peptide production methods vary depending on chain length and application:

• Solid-phase peptide synthesis (SPPS), pioneered by Robert Bruce Merrifield, is widely used for short peptides (<50 amino acids)
• Recombinant DNA technology enables large-scale production of longer peptides such as insulin
• Enzymatic hydrolysis is commonly used in food-grade peptide production

6. Emerging Trends in Peptide Research

• Multifunctional peptides integrating targeting, therapy, and imaging
• Oral peptide delivery systems, including cyclic peptides and nanocarriers
• AI-assisted peptide design, accelerating drug discovery through structure-function prediction

7. Case Insight: Melanotan II

Mechanism of Action

Melanotan II is a synthetic melanocortin receptor agonist that primarily targets MC1R receptors, stimulating melanin production and promoting skin pigmentation.

Applications

• Cosmetic tanning
• Pigmentation regulation research

Market Pricing Dynamics

The pricing of Melanotan II varies significantly depending on production standards and quality levels:

• GMP-grade production: Typically associated with higher purity, regulatory compliance, and consistent batch quality
• Research-grade (non-GMP): Commonly offered at lower prices, often used in laboratory settings

Recent market observations indicate:

• Bulk supply pricing can reach as low as RMB 23/kg under certain supply chain conditions
• Laboratory-grade material may be priced at USD 600–800 per gram, reflecting differences in synthesis scale, purity standards, and supplier positioning

This wide price disparity highlights the importance of: