I am currently trying to compile a meta analysis looking at the influence of enzyme activity of xylanase on fiber digestibility.
However, much of the research I have compiled have different enzyme units reported. The main issue is that most articles do not define U. I know the standard definition of U is defined as the amount of enzyme required to liberate 1 umol of substrate in 1 minute under standard conditions but since articles do not report this and simply give enzyme activity as XX U/kg, I have no way to compare these values. The articles also do not confirm that U is defined as international U (IU).
Was there anything I can do to standardize the enzyme activity in order to analyze the reported data? Alternatively, was there any other type of analysis I could still do with enzyme activity data and fiber digestibility?
Thank you in advance
It seems unlikely to me that you will be able to achieve this goal for published measurements. In addition to there being no standard unit definition, the conditions used are likely to have been different between papers. Reaction conditions (type and source of substrate, temperature, pH, salt composition, etc.) affect enzyme activity. Furthermore, the quantitation of activity will have been affected by the method of measurement and degree of adherence to Michaelis-Menten kinetics.
If you want to do a meaningful comparison between preparations of xylanase, you will have to bring them together in the lab and test them simultaneously under identical conditions.
I agree with Adam. However, depending on your question, you may not have to compare absolute activities. For example, if different labs report the maximal activity under their respective conditions, and the activity in the presence of an inhibitor under the same conditions, then the v/Vmax values may be comparable.
Just an aside: The correct unit of enzyme activity in the SI is not µmol/min (= U), but mol/s (= katal).
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