Zinc-free FTS nonapeptide component

evidence_access

Primary bibliographic record and abstract checked; full methods/figures not comprehensively reviewed.

experimental_contrast

{"intervention": "Radiolabeled FTS binding in 1301/HSB2", "comparator": "Other tested cell lines and assay controls", "endpoint": "Radioligand assays found specific FTS-binding sites with apparent Kd near 3 nM in 1301 and HSB2 cells; several other tested cell lines lacked comparable binding.", "effect_direction": "mixed", "combination": "single", "conditions": []} Explicit extracted experimental comparison; source-derived draft.

experimental_model

Human lymphoblastoid cell lines; binding protein identity unresolved.

interpretation_status

Source-derived extraction of a fact-checked reference; access is explicit, not independent raw-data verification.

limitations

Interpret only within the recorded preparation, exposure and comparator. The complete source passage retains qualifications; unspecified doses/timing have not been extracted here. No clinical efficacy, nutrient deficiency or unique molecular mediation is inferred.

plain_language

Radioligand assays found specific FTS-binding sites with apparent Kd near 3 nM in 1301 and HSB2 cells; several other tested cell lines lacked comparable binding.

primary_references

Specific receptors for the serum thymic factor (FTS) in lymphoblastoid cultured cell lines. | 1980 | DOI 10.1073/pnas.77.5.2861 | PMID 6248873 | https://doi.org/10.1073/pnas.77.5.2861

source_locator

Reviewed reference lines 54-54; exact primary location described in quoted passage where extracted.

Thymulin: detailed mechanisms of action (reviewed 3 October 2026) · lines 54–54

Original AI-assisted review of primary studies and, where relevant, official regulatory records. Access level is retained per claim. Corrections, null results and unresolved questions remain explicit. Not publisher full text or independent replication. · supports · Human lymphoblastoid cell lines; binding protein identity unresolved. · Recorded from source · Recorded from source

Historical radioligand experiments found specific FTS-binding sites in the human lymphoblastoid lines **1301 and HSB2**, with an apparent dissociation constant near 3 nM. Several other tested cell lines lacked comparable binding. This supports selective cellular recognition, but does not identify the binding protein or establish a receptor family. The cellular binding constant and the zinc–peptide binding constant above describe different interactions. [Pleau et al., 1980](https://doi.org/10.1073/pnas.77.5.2861)

evidence_access

Primary bibliographic record and abstract checked; full methods/figures not comprehensively reviewed.

experimental_model

Purified complexes in DMSO-d6; not serum or intracellular occupancy.

interpretation_status

Source-derived extraction of a fact-checked reference; access is explicit, not independent raw-data verification.

limitations

Interpret only within the recorded preparation, exposure and comparator. The complete source passage retains qualifications; unspecified doses/timing have not been extracted here. No clinical efficacy, nutrient deficiency or unique molecular mediation is inferred.

plain_language

NMR in DMSO-d6 identified 1:1 and 1:2 zinc-peptide complexes; Ser4 and the Asn9 terminal carboxylate coordinated zinc, with Ser8 participating in the 1:1 complex.

primary_references

NMR study of a lymphocyte differentiating thymic factor. An investigation of the Zn(II)-nonapeptide complexes (thymulin). | 1988 | DOI 10.1016/s0021-9258(18)60603-9 | PMID 3356698 | https://pubmed.ncbi.nlm.nih.gov/3356698/

source_locator

Reviewed reference lines 27-27; exact primary location described in quoted passage where extracted.

Thymulin: detailed mechanisms of action (reviewed 3 October 2026) · lines 27–27

Original AI-assisted review of primary studies and, where relevant, official regulatory records. Access level is retained per claim. Corrections, null results and unresolved questions remain explicit. Not publisher full text or independent replication. · supports · Purified complexes in DMSO-d6; not serum or intracellular occupancy. · Recorded from source · Recorded from source

The structural qualification matters: the 1988 NMR work was performed in **DMSO-d₆**, not blood. It identified 1:1 and 1:2 zinc–peptide complexes depending on the mixture. Coordination involved Ser4 and the Asn9 **terminal carboxylate**, with Ser8 also participating in the 1:1 complex. This supports a metal-dependent conformation but does not establish the distribution of complexes in living tissues. “One zinc per active peptide” should therefore describe a conventional preparation/activation model, not proven universal physiological occupancy. [NMR study](https://pubmed.ncbi.nlm.nih.gov/3356698/)

evidence_access

Primary bibliographic record and abstract checked; full methods/figures not comprehensively reviewed.

experimental_contrast

{"intervention": "pH below 6", "comparator": "pH 7.5", "endpoint": "Purified FTS bound zinc with apparent Kd (5 +/- 2) x 10^-7 M at pH 7.5; binding was undetectable below pH 6 in this assay.", "effect_direction": "mixed", "combination": "single", "conditions": []} Explicit extracted experimental comparison; source-derived draft.

experimental_model

Purified-system binding assay; pH 7.5 versus below pH 6.

interpretation_status

Source-derived extraction of a fact-checked reference; access is explicit, not independent raw-data verification.

limitations

Interpret only within the recorded preparation, exposure and comparator. The complete source passage retains qualifications; unspecified doses/timing have not been extracted here. No clinical efficacy, nutrient deficiency or unique molecular mediation is inferred.

plain_language

Purified FTS bound zinc with apparent Kd (5 +/- 2) x 10^-7 M at pH 7.5; binding was undetectable below pH 6 in this assay.

primary_references

Studies on the zinc binding site to the serum thymic factor. | 1984 | DOI 10.1016/0304-4165(84)90116-8 | PMID 6538097 | https://pubmed.ncbi.nlm.nih.gov/6538097/

source_locator

Reviewed reference lines 25-25; exact primary location described in quoted passage where extracted.

Thymulin: detailed mechanisms of action (reviewed 3 October 2026) · lines 25–25

Original AI-assisted review of primary studies and, where relevant, official regulatory records. Access level is retained per claim. Corrections, null results and unresolved questions remain explicit. Not publisher full text or independent replication. · supports · Purified-system binding assay; pH 7.5 versus below pH 6. · Recorded from source · Recorded from source

A separate binding study reported an apparent zinc dissociation constant of **(5 ± 2) × 10⁻⁷ M at pH 7.5** and no detectable binding below pH 6 under its assay conditions. Other tested metals competed for binding. These are purified-system measurements, not a threshold for dietary intake, plasma zinc or thymulin failure inside a patient. They make pH and competing ligands relevant experimental variables. [Zinc-binding study, 1984](https://pubmed.ncbi.nlm.nih.gov/6538097/)

evidence_access

Primary bibliographic record and abstract checked; full methods/figures not comprehensively reviewed.

experimental_contrast

{"intervention": "Zinc addition to metal-depleted FTS", "comparator": "Metal-depleted FTS", "endpoint": "Zinc addition restored classical thymulin rosette-bioassay activity after Chelex metal removal, with best activation at a 1:1 metal-to-peptide ratio.", "effect_direction": "increase", "combination": "single", "conditions": []} Explicit extracted experimental comparison; source-derived draft.

experimental_model

Purified peptide and classical rosette bioassay; Chelex metal removal followed by metal reconstitution.

interpretation_status

Source-derived extraction of a fact-checked reference; access is explicit, not independent raw-data verification.

limitations

Interpret only within the recorded preparation, exposure and comparator. The complete source passage retains qualifications; unspecified doses/timing have not been extracted here. No clinical efficacy, nutrient deficiency or unique molecular mediation is inferred.

plain_language

The peptide needs appropriate zinc association to be active in this assay; zinc is not shown to be consumed by signaling.

primary_references

Contribution of zinc and other metals to the biological activity of the serum thymic factor. | 1982 | DOI 10.1073/pnas.79.17.5370 | PMID 6957870 | https://doi.org/10.1073/pnas.79.17.5370

source_locator

Reviewed reference lines 23-23; exact primary location described in quoted passage where extracted.

Thymulin: detailed mechanisms of action (reviewed 3 October 2026) · lines 23–23

Original AI-assisted review of primary studies and, where relevant, official regulatory records. Access level is retained per claim. Corrections, null results and unresolved questions remain explicit. Not publisher full text or independent replication. · supports · Purified peptide and classical rosette bioassay; Chelex metal removal followed by metal reconstitution. · Recorded from source · Recorded from source

In the foundational experiments, Chelex-mediated metal removal abolished rosette-bioassay activity, and zinc addition restored it. The best activation occurred at a 1:1 metal-to-peptide molar ratio; some other metals produced smaller recoveries. This establishes zinc-dependent activation under those conditions, not a claim that zinc is consumed with every signaling event or that all alternative complexes are inactive. [Dardenne et al., 1982](https://doi.org/10.1073/pnas.79.17.5370)