|MadSci Network: Biochemistry|
If I understand you, what you want to do is collect some tissues and assay them all at once at the end of your experiment. That's a smart way to do it, because it minimizes variation due to buffer composition, technique, etc. You shouldn't have a problem with freezing renal tissue and assaying it for caspase activity upon thaw. I've never done the particular assay you mention, and I don't know the sample work-up requirements, but I know that caspase 3 itself is fairly stable. If you harvest the tissue, place it in a clean cryotube, then immediately submerge the tube in liquid nitrogen, it should keep for years. When you thaw it out, you may want to do so in a small amount of protease inhibitor cocktail if the assay permits.
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