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Study · In vitro (cell-free) · 1991

3 results

Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable.

Safer D, Elzinga M, Nachmias VT

The Journal of biological chemistry1 Mar 1991Cited by 270 (Europe PMC)

PMID1999398 (opens in a new tab)DOI10.1016/s0021-9258(20)64278-8 (opens in a new tab)PepBankPUB-01999398
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Summary

At least 50% of the actin in resting human platelets is unpolymerized, and the bulk of this unpolymerized actin is complexed with a recently identified acidic, heat-stable 5-kDa peptide, named "Fx." Purified Fx binds stoichiometrically to muscle G-actin, forming a complex identifiable by nondenaturing polyacrylamide gel electrophoresis. Formation of the complex inhibits salt-induced polymerization of G-actin. Here we report that Fx is indistinguishable from thymosin beta 4, an acidic, heat-stable 5-kDa peptide first isolated from calf thymus and thought to be a thymic hormone. The complete amino acid sequence of Fx was determined and was found to be identical with that of thymosin beta 4. Authentic thymosin beta 4 is functionally equivalent to Fx, forming a 1:1 complex with actin monomers and inhibiting polymerization. The widespread distribution and high intracellular concentration of thymosin beta 4 (Fx) strongly suggest that it plays a significant role in regulating actin polymerization in many cell types.
CC BYText from Europe PMC. Highlighted sentences are the source of results.

Results from this study3

2 results from studies that gave the peptide. No result from this study comes from people.

  1. 01LabIn vitro (cell-free)Activity measurement

    In cell-free tests, authentic thymosin beta‑4 formed a 1:1 complex with actin monomers, as Fx does.

    In plain wordsIn lab tests, thymosin beta‑4 bound actin monomers one to one.

    Peptide
    Thymosin beta-4 (human)
    Outcome
    Not applicableComplex formation of thymosin beta 4 with actin monomers
    Study

    n: not reported in source

    Purified peptide and muscle G-actin, cell-free
    Outcome group
    Receptor activity and mechanism · Whole body
    Studied dose
    Dose not stated

    Source sentences

    Summary
    Authentic thymosin beta 4 is functionally equivalent to Fx, forming a 1:1 complex with actin monomers and inhibiting polymerization.
    1 context sentence
    Summary · context
    At least 50% of the actin in resting human platelets is unpolymerized, and the bulk of this unpolymerized actin is complexed with a recently identified acidic, heat-stable 5-kDa peptide, named "Fx."
  2. 02LabIn vitro (cell-free)Activity measurement

    In cell-free tests, authentic thymosin beta‑4 inhibited actin polymerization.

    In plain wordsIn lab tests, thymosin beta‑4 stopped actin from forming filaments.

    Peptide
    Thymosin beta-4 (human)
    Outcome
    DecreaseInhibition of actin polymerization by thymosin beta 4
    Study

    n: not reported in source

    Purified peptide and muscle G-actin, cell-free
    Outcome group
    Receptor activity and mechanism · Whole body
    Studied dose
    Dose not stated

    Source sentences

    Summary
    Authentic thymosin beta 4 is functionally equivalent to Fx, forming a 1:1 complex with actin monomers and inhibiting polymerization.
    1 context sentence
    Summary · context
    At least 50% of the actin in resting human platelets is unpolymerized, and the bulk of this unpolymerized actin is complexed with a recently identified acidic, heat-stable 5-kDa peptide, named "Fx."

Studies that did not test the peptide alone1

In this study, Thymosin beta-4 (human) was a lab tool or a carrier, part of a mix, or the subject of a lab method. These results are not evidence about taking Thymosin beta-4 (human).

  1. 03LabNot a test of Thymosin beta-4 (human) aloneIn vitro (cell-free)Other

    The complete amino acid sequence of Fx was identical with that of thymosin beta‑4.

    In plain wordsIn lab tests, a peptide from human platelets called Fx had the same sequence as thymosin beta‑4.

    Peptide
    Thymosin beta-4 (human)
    Outcome
    Not applicableAmino acid sequence of Fx compared with thymosin beta 4
    Study

    humann: not reported in source

    Fx peptide from human platelets
    Outcome group
    Receptor activity and mechanism · Whole body

    Source sentences

    Summary
    The complete amino acid sequence of Fx was determined and was found to be identical with that of thymosin beta 4.
    1 context sentence
    Summary · context
    At least 50% of the actin in resting human platelets is unpolymerized, and the bulk of this unpolymerized actin is complexed with a recently identified acidic, heat-stable 5-kDa peptide, named "Fx."

    In this study, Thymosin beta-4 (human) was a lab tool or a carrier, part of a mix, or the subject of a lab method. This result is not evidence about taking Thymosin beta-4 (human).

AI wrote and checked these results. AI can make mistakes, so check important results against the source.

Version history

PepBank keeps every version of the data on this study. Status changes from Retraction Watch, Europe PMC and Crossref are listed with their source.

  1. Version 2Current

    13 Oct 2026, 01:52 UTC

    Study results updated

  2. Version 1

    12 Oct 2026, 18:17 UTC

    First added · source update from Europe PMC

Subjects

Terms as the source lists them.

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