TGF beta family proteins and other growth factors can be very poorly soluble in physiological solutions.  Please follow the handling guidance for lyophilized cytokines below to minimize loss of protein due to precipitation or adsorption to plastic.  We advise storing the recombinant protein at very low pH before dilution in cell culture media or final working solutions. Low pH will also assist in maintaining the correct disulfide structure of the protein by minimizing disulfide bond exchange reactions.
Resuspension in physiological buffers may cause precipitation of stock solutions, hence we recommend dissolving our lyophilized cytokines in 10 mM HCl (1:1000 dilution of concentrated HCl) while keeping the protein concentration at 50 µg/ml or above, in order to avoid loss by adsorption to plasticware.
To ensure you recover all of the protein, let the sample sit for a few minutes with the solubilization buffer at room temperature and pipette gently up and down (avoid foaming).
Rinse the tube with some more 10 mM HCl and pool with the rest.
The protein is tolerant of some freeze and thaw cycles, but as always with proteins, it is better to aliquot and store frozen.
Our proteins are supplied carrier-protein free.  If compatible with your work, add carrier protein of your choice such as BSA, HSA or gelatin to further minimize loss by adsorption.
Store in -80°C for long term storage. -20°C for short-term.
Every effort is made to ensure samples are sterile; however, we recommend sterile filtering after dilution in media or the final working solution.