Re: How to convert a concentration of an enzyme of units/ml to mg/ml?

Dear Cynthia,

Thanks for your question. The brief answer is that you cannot calculate the conversion from the data that you have given. If you think about it, on one side we have Units/ml and on the other, mg/ml. The only way to relate these two variables is if we also know Units/mg. For instance, if we knew that the enzyme activity was 2000 U/mg, then 100 000 U/ml would equate to 50 mg/ml and you would need to dilute your enzyme 5-fold to achieve 10 mg/ml.

If you don't have a value for activity in U/mg, forget about units altogether! Do a protein concentration assay of your enzyme preparation (such as a Bradford assay) and dilute as required.

My advice to you when dealing with biochemical calculations is:

• Don't panic. Most calculations in biochemistry are quite simple.
• Think about the problem logically and try to figure it out before you go surfing the web for a solution. In your example, I think that you'd have figured out the requirement for data in U/mg with a little thought.
• Learn how to search effectively online. There are plenty of undergrad biochemistry courses and biochemical protocols online. A Google search using "convert enzyme units mg/ml" took me straight to this page, which is essentially identical to your question.
• Get yourself a good clear textbook. I own a book titled "Biochemical Calculations 2nd Edition" by I. Segel. It's a classic text from 1976 (which sounds really ancient!) so it may not be available now, but I found it to be very clear, simple and helpful when I was an undergrad. Find a book that works for you.

Hope that this helps you,
Neil