[nj_bartel]

Q.  The action of methylmalonyl CoA mutase is an isomerization that could occur by moving either COO^- or -CO-CoA.  Design and describe an experiment that would distinguish between these cases.

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I don't see how this can be done isotopically or any other way honestly.  At least not in a way that would be an acceptable test answer, because doing something like altering the functional groups to prevent them from reacting could prevent enzyme action altogether.

Any ideas?

[cpncoop]

The most common way to do this (I believe) would be to make the 13C labeled compound and then analyze it with high res mass spec to see how it fragments.  The two compounds will fragment differently dependent upon the isomerization.  I suppose you could also try a chemical modification of one of the functional groups to see if it shuts down isomerization, but as you mentioned, that may kill enzyme activity.

[nj_bartel]

Thanks for the reply.  We got answers back today - the answer was to dope the initial compound's methyl group with 14-C, an isotope I wasn't aware of D: