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    Ingredient guide · Ingredient reference

    Mature human insulin: the A and B amino-acid sequences

    Mature human insulin contains a 21-residue A chain and a 30-residue B chain. The 110-residue sequence in the human INS precursor record includes additional regions removed during processing.

    Read the evidence ↓

    Supplement Science Insights Editorial Team

    Published September 23, 2026

    Read each chain from its own amino terminus

    The A-chain sequence is GIVEQCCTSICSLYQLENYCN. The B-chain sequence is FVNQHLCGSHLVEALYLVCGERGFFYTPKT. These are one-letter amino-acid codes for mature human insulin. [1]

    UniProt annotates the B chain at precursor positions 25–54 and the A chain at positions 90–110. Those precursor coordinates should not be mistaken for numbering within the mature chains. [1]

    The precursor is not the finished hormone

    MedlinePlus describes processing of proinsulin into A and B chains connected by disulfide bonds. The curated sequence record also distinguishes a signal peptide and the mature-chain features. [1][2]

    A 110-residue precursor and a 51-residue mature hormone therefore do not represent conflicting counts. Also specify human insulin when comparing sequences: an engineered insulin analogue need not have the same sequence or modifications. [1][2]

    Use inclusive coordinates correctly

    The precursor interval 25–54 contains 54 minus 25 plus 1, or 30 residues. The interval 90–110 contains 21. Together they account for the 51 residues of the mature A and B chains.

    Key distinctions — Mature human insulin
    DetailInterpretation
    A chain21 residues
    B chain30 residues
    Precursor110 residues before processing
    Mature human insulin: the A and B amino-acid sequences — original article outline diagram
    Original editorial diagram of this article’s sections; no product photograph or clinical finding is depicted.

    Sources for this article

    1. UniProt P01308 — human insulin, reviewed sequence and processing annotations
      Source consulted: 2026-09-17. This is a reference resource, not a claim that we conducted the studies or tested a product.
    2. INS gene: MedlinePlus Genetics
      Source consulted: 2026-09-17. This is a reference resource, not a claim that we conducted the studies or tested a product.