Disulfide Bond
Definition
A covalent bridge between the sulfur atoms of two cysteine residues. It staples distant parts of a chain together and holds a fold in place, and reducing conditions break it, which is one way a peptide loses activity without losing mass.
In more detail
A disulfide bond is a covalent link between the sulfur atoms of two cysteine side chains, formed by oxidation. It ties two points of a chain together and is a principal reason a folded peptide holds its shape.
Where a molecule contains several cysteines, the pairing is part of its identity: the same sequence with the bridges joined differently is a different molecule with the same mass, and mass spectrometry alone will not separate them. Synthesising one deliberately uses protecting groups removed in a chosen order rather than letting the pairs find each other.
The bond is reversible. Reducing conditions break it and return the cysteines to free thiols, which is also how an unintended dimer forms when two separate molecules bridge to one another instead of folding.
What this means for research sourcing
Structure and identity terms are what a certificate of analysis is written in. Every Volta compound ships with its sequence, molecular weight and measured purity, so these terms map directly onto the specification on the product page.
Related Terms in Chemistry & Structure
Cysteine
The amino acid whose thiol side chain forms disulfide bridges. It is also one of the three residues most readily oxidised, so a sequence containing it has a predictable degradation liability.
Peptide Fragment
A section cut from a longer peptide or protein and studied on the assumption that it carries part of the parent's activity. The assumption is not automatic: a fragment can retain binding and lose function, or do neither. HGH Fragment 176-191 is named for the residues it spans.
Peptidomimetic
A molecule built to reproduce what a peptide does without being one, often by replacing amide bonds with linkages proteases cannot cut. The point is stability and absorption rather than novelty of target.
Synthetic Peptide
A peptide assembled chemically, in practice almost always by solid-phase synthesis, rather than extracted from tissue or expressed in cells. Research peptides are overwhelmingly synthetic, which is also why their identity can be checked against a known sequence.
Solid-Phase Peptide Synthesis (SPPS)
The standard way peptides are made: the chain is anchored to a resin bead and extended one protected residue at a time, then cleaved off and purified. Coupling efficiency compounds over the chain, so yield and purity both fall as length rises.
Yield
How much purified peptide a synthesis produced, as a percentage of the theoretical maximum. Low yield raises cost per milligram and tends to travel with a harder purification, which is why long or difficult sequences are expensive.
Molecular Weight
The mass of one molecule, in daltons or g/mol. For a peptide it follows arithmetically from the sequence, so a stated weight that does not match the stated sequence is a contradiction on the page and a reason to look harder at the rest of the document.
Kilodalton (kDa)
One thousand daltons, the unit used once a molecule is large enough that daltons become unwieldy. Short peptides are quoted in daltons; proteins and fusion constructs in kDa.