This product is not specifically tested for solubility. However, as mentioned on the Product Datasheet, the material is expected to be soluble at 0.5 mg/mL in 20mM phosphate-buffered saline containing 6mM Sodium Chloride, pH 6.9. This information is according to the following reference:
Irondi, F.A. et al., Food Sci. Nutr., 5(2), 233-242 (2017).
For analytical purposes, this enzyme is prepared at 1 unit/mL in sold deionized water in the determination of enzymatic activity.
Please see the link below to review the product datasheet for additional information:
https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/product/documents/966/306/a3176pis.pdf