This material is soluble in water, a rate has not been established. For assay purposes, this product is reconstituted at 10 units/100ul in 28.6 mM Barbital buffer (see product B5934) containing 1.0% (w/v) Bovine Serum Albumin and 0.5% (w/v) Polyethylene Glycol, pH 7.35. Please see the link below to review the product datasheet which includes detailed preparation instructions.
https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/product/documents/320/022/h0393pis.pdf
The activity specification for this product is minimum 7000 units per milligram protein. Occasionally, a small amount of powder may not be visible. A gentle spin or ‘shake down’ of the vial may move the powdered product to the bottom of the vial.