Knowledge base
What are peptides?
A peptide is a short chain of amino acids. Peptides occur throughout nature and are studied widely in laboratories. This article explains how a peptide is built, how it differs from a protein, how research peptides are made and what the names and abbreviations mean.
Amino acids: the building blocks
Amino acids are small molecules with an amino group, an acid group and a side chain that differs per amino acid. Proteins use twenty standard amino acids, each with a three-letter code (Gly for glycine, Lys for lysine) or a one-letter code (G, K).
The side chain determines the properties: some amino acids are basic (lysine, arginine), others acidic (aspartic acid, glutamic acid) or water-repellent. That mix decides, among other things, how well a peptide dissolves.
The peptide bond
Two amino acids join through a peptide bond: the acid group of one amino acid reacts with the amino group of the next, releasing water. This gives a chain with a start (the N-terminus) and an end (the C-terminus). The order of the amino acids is called the sequence and is written from the N- to the C-terminus.
Peptide or protein?
Examples from the range: GHK-Cu is a tripeptide with copper, Semax and Selank are heptapeptides and BPC-157 is a chain of fifteen amino acids.
- A dipeptide consists of two amino acids, a tripeptide of three, a pentapeptide of five and a heptapeptide of seven.
- Chains of up to about fifty amino acids are usually called peptides, longer chains proteins. The boundary is a convention, not a hard rule.
- A protein usually folds into a fixed three-dimensional shape. Many short peptides have no such fixed fold.
How are research peptides made?
Most research peptides are made chemically by solid-phase peptide synthesis (SPPS), a method Bruce Merrifield described in 1963. The chain is built one amino acid at a time on a small resin bead, after which the peptide is released from that support.
The crude peptide is then purified by HPLC and freeze-dried to a powder. At every coupling a small share of the chains can miss an amino acid. Those related chains are the main impurities, and they are exactly what an HPLC analysis measures.
Names and abbreviations
- A code such as BPC-157 or TB-500 is a historical or trade name, not a description of the structure.
- Ac- at the start of a sequence means the N-terminus is acetylated; -NH2 at the end means the C-terminus is an amide.
- A D- before an amino acid (such as D-Ala) marks the mirror-image form, which enzymes break down more slowly.
- Acetate or TFA on a certificate is the counter-ion: the salt in which the peptide was freeze-dried after purification.
What to look for as a researcher
Because a peptide is an exact sequence, every lot should come with an analysis showing its identity (mass) and purity. How to read such a report is explained in Reading a lab report; BrabantLabs certificates are on Lab results. What else to look for when buying is in Buying research peptides in the Netherlands.
Frequently asked questions
- What is the difference between a peptide and an amino acid?
- An amino acid is a single building block; a peptide is a chain of two or more amino acids joined by peptide bonds.
- How many amino acids does a peptide have?
- From two to about fifty. Longer chains are usually called proteins, although that boundary is a convention.
- Why are peptides supplied as a powder?
- Freeze-dried, a peptide is far more stable than in solution. You only dissolve a vial when you need it.
- Is a synthetic peptide the same as a natural one?
- A synthetic peptide with the same sequence and the same modifications is chemically the same molecule. Whether it is, the mass measurement (MS) on the certificate shows.
In the shop
For laboratory research only. BrabantLabs products are intended for laboratory research and not for human or animal use. This article describes what has been published in the scientific literature and is not a health claim or advice on use.