If you have the information of the enzyme's specific activity in units/mg of protein, then you can convert U/ml to mg/ml. Lacking this information, you will just have to measure the protein concentration by BCA protein assay, using a standard protein to make a standard curve. People usually use bovine serum albumin as the standard protein.

You can calculate your protein content per ml of sample, then enzyme-specific activity - unit per mg of protein.

Thank u for answering my question.

As said above quantify the total protein content using BSA as standard and you can convert units to mg/ml