I'm trying to understand why % yield is measured with activity instead of total protein in mg. According to my biochemistry notes, activity is "1.0 units of enzyme activity = 1.0 μmol of substrate catalyzed to product under optimum conditions."

Then, yield is defined as "% of total starting protein/enzyme in final purified protein fraction."

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With this definition of yield, it would make sense to say that you get 30% yield in the second step since you have 3,000 mg / 10,000 mg of the original protein amount. The definition of yield in my notes mentions nothing of activity.


1 Answer 1


Because total protein includes other proteins than the one desired.

"% yield" is expressing how much of the enzyme desired was actually recovered.

  • $\begingroup$ Oh duh. Thank you. Activity is talking about a specific reaction with your desired protein. Thanks! $\endgroup$
    – 5antoro
    Feb 9, 2017 at 21:07

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