When do enzymes stop reacting to the substrates?

If the reaction is divalent metal ion-dependent, you can stop the reaction by adding an excess of EDTA to bind the metal.

You can kill the protein by adding perchloric acid, then precipitate the perchlorate with an equivalent amount of potassium carbonate, leaving nothing but carbonic acid in the supernatant, which bubbles off as carbon dioxide. Centrifuge the sample and take the supernatant to analyze for the product.

A rather slow method is ultrafiltration, using a micro-centrifugal ultrafilter (e.g. Microcon) with a molecular weigh cutoff smaller than the molecular weight of the enzyme. This can be done at 4oC to slow down the reaction during the separation.

Explanation:

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