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Pioneering proteins combining academic innovation and high purity manufacture at Qkine

Recombinant human/mouse/rat follistatin-resistant Activin A protein (Qk035)

Follistatin-resistant activin A protein (FRACTA) has been engineered to prevent binding to the natural inhibitor, follistatin.  Activin A activity protein is regulated in vivo by follistatin, a high-affinity inhibitor; follistatin accumulates in stem cell culture, where it inhibits activin A.

Qk035 follistatin-resistant activin A protein (FRACTA) has equivalent bioactivity to wild-type activin A (Qk001) but does not bind follistatin so is resistant to feedback inhibition. High purity 26 kDa dimer comprising engineered mature domain of activin A protein, animal-free (AF) and carrier-protein free (CF). This specialised activin A has been developed in Marko Hyvönen’s group in the University of Cambridge.

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1mg will be despatched as 2 x 500µg


  • High purity mature domain of follistatin-resistant activin A protein

  • >98%, by SDS-PAGE quantitative densitometry

  • 26 kDa (dimer)

  • Expressed in E. coli

  • Animal-free (AOF) and carrier protein-free.

  • Manufactured in our Cambridge, UK laboratories

  • Lyophilized from acetonitrile, TFA

  • Resuspend in 10mM HCl at >100 µg/ml (provided with protein and free of charge), prepare single use aliquots, add carrier protein if desired and store frozen at -20°C or -80°C


follistatin resistant activin A Qk035 protein bioactivity lot #104287

Activin A protein activity is determined using an activin-responsive firefly luciferase reporter in HEK293T cells.  EC50 for wild-type activin A (Qk001) = 0.228 ng/ml (8.776 pM), EC50 for follistatin-resistant activin A (FRACTA, Qk035) = 0.228 ng/ml (8.792 pM).


follistatin resistant activin A FRACTA Qk035 protein purity lot #104287

FRACTA migrates as a single band at 24 kDa in non-reducing (NR) and 13 kDa as a single monomeric species upon reduction (R).  No contaminating protein bands are visible.

Purified recombinant protein (1 µg) was resolved using 15% w/v SDS-PAGE in reduced (+β-mercaptothanol, R) and non-reduced conditions (NR) and stained with Coomassie Brilliant Blue R250.  Data from Qk035 lot #104287.

Further quality assays

  • Mass spectrometry: single species with expected mass

  • Analytical reversed-phase: single sharp peak

  • Endotoxin: <0.005 EU/μg protein (below level of detection)

  • Recovery from stock vial:  >95%

We are a company founded and run by scientists to provide a service and support innovation in stem cell biology and regenerative medicine.  All our products are exceptionally high purity, with complete characterisation and bioactivity analysis on every lot.

negative feedback inhibition of activin A by follistatin

Protein background

Human Activin A protein is a member of the TGFβ superfamily of growth factors involved in stem cell differentiation and maintenance, regulation of embryogenesis, development of the reproductive system, wound healing and regulation of immune responses.  Activin A signalling is modulated by the glycoprotein follistatin, production is which is stimulated by Activin A forming a feedback loop (1) , and inhibins.

Follistatin binds to and neutralises members of the TGF-β superfamily, preventing signalling by shielding the type II and I receptor binding sites (2-4).

Activins are disulfide-linked homo- and heterodimers of four inhibin β chains. The best characterized are Activin A and Activin B, homodimers of inhibin βA and inhibin βB respectively. Activins, like all other members in the TGF-β superfamily, are synthesized as larger precursors consisting of an N-terminal signal peptide, a pro-domain of 250–350 residues and a highly conserved mature domain. The pro-domain, which is cleaved off in the mature protein, has important roles in the biosynthesis, stabilization, transportation and signalling of the growth factors (5).

Recombinant Activin A is used for maintenance of pluripotency in many human induced-pluripotent stem cell and human embryonic stem cell lines3, and to induce stem cell differentiation into endoderm(6)  and other cell fates.

Follistatin resistant activin A (FRACTA) has been developed in the lab of Marko Hyvönen at the University of Cambridge. FRACTA has been engineered to be unimpeded by follistatin while maintaining its ability to bind type I and II receptors.

Our products are for research use only and not for diagnostic or therapeutic use.  Products are not for resale.

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