Does anyone have any experience with storing solutions of GDH/TPI for use in coupled enzyme kinetic assays? A couple of sources suggest the solution has to be prepared fresh and can lose activity in as short as 15 minutes! Not only would this waste a lot of reagent, but it also makes the assay basically impossible to perform (not sure I can set everything up that quickly, and if something goes wrong then the whole pot is wasted). It's supplied as an ammonium sulphate suspension and it's not practical to weight out amounts smaller than 1 mg so I would need to use the whole stock of it to prepare reagent for a single day, and most of it wouldn't be used.
Has anyone tried freezing it with BSA/glycerol or storing it in the fridge for up e.g. up to about a week?
Since the reagent is supplied as an ammonium sulfate suspension, you do not have to weigh it out. You can just stir it up and use a pipettor to withdraw the necessary volume of the suspension. If the suspension is going to be greatly diluted in the assay buffer, you may be able to use it "as is." However, if you need to get rid of most of the ammonium sulfate, then all you have to do is centrifuge the volume that you withdrew in a microcentrifuge (without diluting it first), then dissolve the pellet in the desired buffer.
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