The reaction catalyzed by carbonic anhydrase is carbon dioxide + water bicarbonate. There are multiple isozymes, all performing the same reaction, expressed in a tissue-specific manner, with CAIII expression mainly in skeletal muscle. I can't see how you could directly measure the enzymatic activity of CAIII selectively in vivo in any simple way. The amount of CAIII protein can be assayed immunologically. Perhaps you could measure a downstream effect of inhibiting the activity of CAIII in vivo, or make a tissue extract and assay the CA activity in the extract. However, if you do make an extract and your inhibitor is reversible, the resulting dilution will cause the inhibitor to dissociate and lose potency.

There are some pretty sophisticated ways of measuring CA activity in vivo using isotopic labels. See these references, for example.

http://cancerres.aacrjournals.org/content/early/2015/09/17/0008-5472.CAN-15-0857.abstract

https://www.researchgate.net/publication/248149693_Carbonic_anhydrase_activity_in_leaves_as_measured_in_vivo_by_18_O_exchange_between_carbon_dioxide_and_water

Article Carbonic anhydrase activity in leaves as measured in vivo by...

unfortunately this method is difficult to be applied in our institution. I have found some articles using Immuno- staining for the enzyme to detect enzyme expression in skeletal muscles, but I am not testing the expression.

would you mind explain more about immunological method to investigate CAIII?

there are around 12 isozyme of Carbonic anhydrase, and they are expressed widely in the body, and I am concerned with the isozyme III.

can you explain more?

Appreciated

There are ELISA kits available for measuring the amount of CAIII protein in extracts of muscle. Here are examples:

https://www.lsbio.com/elisakits/human-ca3-carbonic-anhydrase-iii-elisa-kit-sandwich-elisa-ls-f7373/7373

http://www.uscnk.com/uscn/ELISA-Kit-for-Carbonic-Anhydrase-III--Muscle-Specific-%28CA3%29-7110.htm