I need to store organ for my research, but I can not get my ELISA kit reagent about 2 months after I decapitate the rats? How can I store organ with minimal protein change? I have -20 degree Celsius refrigerator.
Usually, we sacrificed the animal then we immediately remove the organ (in our case the brain) before snap freeze it into liquid nitrogen or into dry ice mixed with ethanol. For +/- long term storage -20 is fine, I haven't seen differences in my ELISA results between fresh brain homogenates or 2-3 months. But, it depends of your protein stability of course!
I don't know specifically for TGF beta, but some proteins can be highly sensitive to temperature and/or light. So, if you immediately snap freeze your tissue and store it at -20oC (or -80oC it's even better) you'll have minimal degradation.