The Chitinase is provided based on units of activity, and the protein mass will vary for individual lots. The specification states that the specific activity will be ≥ 50.00 units per mg protein. The specification sheet can be found here:
https://www.sigmaaldrich.com/specification-sheets/176/740/C9830-10UN________SIGMA____.pdf
The Data Sheet provides the following reconstitution instructions:
Prepare a stock solution by reconstituting a 10 unit vial with 300 ul of water. For long term solution storage reconstitute vial with 50% glycerol solution.
https://www.sigmaaldrich.com/deepweb/assets/sigmaaldrich/product/documents/285/698/c9830dat.pdf