EVIDENCE DESKTOP // ZINC-BOUND THYMIC FACTOR
Thymulin is the zinc-bound thymic nonapeptide whose activity switches off without zinc.
One zinc ion, bound 1:1, is the whole story. Bound: active. Absent: inactive. This desktop reads the published record straight — every claim cited, every tier marked, every gap left in plain view.
The short version
Thymulin is a small hormone made by the thymus, the immune-training gland behind the breastbone. It is a nonapeptide (a chain of nine amino-acid building blocks), and it only switches on when a single zinc atom is attached. Strip the zinc out and the peptide goes dark; add it back and the peptide wakes up [1]. Studied since the 1980s, thymulin's classical job is helping T cells (the immune system's trained defender cells) mature [11]. It is a research peptide. It is not FDA-approved, and it is not a dietary supplement.
What thymulin is
Thymulin is a zinc-dependent thymic nonapeptide hormone, produced exclusively by thymic epithelial cells (the gland's lining cells that build it) [11]. Sequence: pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn. Molecular weight: 858.86 Da. CAS: 63958-90-7. It is biologically active only when bound to one zinc(II) ion in a 1:1 molar ratio — the defining mechanistic fact, established in the original work that coined the name [1].
The zinc-free form is inactive. In the 1982 paper that named thymulin, treating the peptide with the chelator Chelex 100 (a resin that strips metal ions out) abolished its activity in a cell-based assay; adding zinc salts back restored it, with a 1:1 metal-to-peptide ratio giving optimal activation [1]. Antibodies raised against the zinc-coupled form block activity, confirming that zinc builds the active three-dimensional shape, not just a passenger ion [4].
The name carries a history. Before 1982 the same molecule was called serum thymic factor, or FTS, from the French facteur thymique serique [1]. FTS was the zinc-free peptide; thymulin is what it becomes when zinc binds. So the older papers on FTS and the newer ones on thymulin are reading the same nonapeptide — a point worth holding onto, because a lot of the foundational work is filed under the earlier name [6][7].
Circulating thymulin is present from birth, peaks in childhood, and falls with age and with zinc deficiency [11]. Read the full mechanism on thymulin research findings, the zinc story in depth at zinc thymulin, or why thymulin needs zinc laid out as an on/off switch. One caution up front: thymulin is not thymosin alpha-1 — see thymulin vs thymosin alpha-1 for why the two are routinely, and wrongly, conflated.
Thymulin Peptide: Structure and Identity
STRUCTURE: linear nonapeptide. SEQUENCE: pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (also written <Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn). FORMULA: C33H54N12O15. MW: 858.86 Da.
The thymulin peptide is small, and small peptides clear fast — one reason gene-therapy strategies were later built to sustain circulating levels rather than dose the bare peptide [12]. Its activity is not a property of the sequence alone. Zinc binding drives a specific conformation detected by NMR; the apopeptide (the zinc-free form) has no biological activity until zinc is restored [2]. That is the single fact that separates thymulin from a list of nine amino acids: it is a metallopeptide, and the metal is obligatory [3].
Is thymulin the same as serum thymic factor (FTS)?
Yes, in lineage. "Serum thymic factor" (FTS, from the French facteur thymique serique) is the original name for the same peptide. FTS denotes the zinc-free peptide; once zinc binds 1:1, the active form was named thymulin (FTS-Zn) in the 1982 work [1]. The high-affinity receptors found on T-lineage cells in 1980 were described as FTS receptors — the same molecule, the earlier name [7].
Thymulin, in quick answers
The most-asked questions, answered plainly. The full set lives on the common thymulin questions page.
What is thymulin?
Thymulin is a zinc-dependent thymic nonapeptide hormone produced exclusively by thymic epithelial cells; it is biologically active only when bound to zinc in a 1:1 ratio [1]. It is studied as a research peptide and is not FDA-approved. It is distinct from thymosin alpha-1 and thymosin beta-4 [15].
What is thymulin peptide?
Thymulin peptide is the linear nonapeptide pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn, which becomes biologically active only after binding one zinc ion per molecule [1]. Its molecular weight is 858.86 Da; its formula is C33H54N12O15. The zinc-free form has no activity until zinc is restored [2].
What is the amino acid sequence of thymulin?
Thymulin is the nonapeptide pyroGlu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn (also written <Glu-Ala-Lys-Ser-Gln-Gly-Gly-Ser-Asn), with molecular formula C33H54N12O15 and a molecular weight near 858.86 Da [2].
Is thymulin a hormone?
Yes. Thymulin is a thymic peptide hormone: secreted by thymic epithelial cells, it acts on distant targets, including a hypophysiotropic (pituitary-directed) action within the thymus-neuroendocrine axis [11][10]. Its classical target is the maturing T-cell compartment [3].
Is thymulin produced naturally in the body?
Yes. Thymulin is produced exclusively by thymic epithelial (reticulo-epithelial) cells; circulating levels are present from birth, peak in childhood, and decline with age and zinc deficiency [11].
What does thymulin do in the body?
Endogenously, thymulin contributes to T-lymphocyte differentiation and immune-cell modulation [3][6] and acts as a hypophysiotropic peptide in a bidirectional thymus-neuroendocrine axis [11][10]; circulating levels peak in childhood and fall with age and zinc deficiency [11].
What the record shows, in one screen
ZINC SWITCH: established. Chelate the zinc, activity goes to zero; replete it 1:1, activity returns [1]. CONFORMATIONAL EPITOPE: established. Zinc builds a distinct 3D epitope; antibodies to it block activity [4]. T-CELL DIFFERENTIATION: established in cells. Synthetic thymulin induced T-cell markers on human bone-marrow precursors in vitro [6]. RECEPTOR: established. High-affinity, T-lineage-specific receptors, Kd near 3 nM [7]. HUMAN ZINC LINK: established in humans. In mild zinc deficiency, serum thymulin activity fell despite normal plasma zinc and was corrected by zinc repletion [5].
GAP: human half-life — not established in the public literature [12]. GAP: human efficacy — no large modern trials; the human record is sparse and dated. Everything below the immune and anti-inflammatory headings is a finding in a named species or an in-vitro system, not a demonstrated human outcome.
The newer work is gene therapy. A single inhaled dose of thymulin-expressing plasmids, given after experimental asthma was fully established in mice, normalized the key lung pathologies at 20 days [14]. An animal model — and one of the strongest single results in the file. See it appraised on thymulin and immune function and thymulin research findings.