Hi Dileep,

the half life of HIF proteins at atmospheric oxygen concentrations is about five minutes; therefore you should harvest the tissues within a couple of minutes. I hope this helps. Good luck! Here is publication for a protocol to isolate HIFs from human brain tissue .Zhang, X., Huang, C. J., Nazarian, R., Ritchie, T., de Vellis, J. S., Noble, E. P. (1997) Isolation of nuclear proteins from human brains. BioTechniques 22,848-850

Johnny

I found out another  protocol which might be more close to isolation of HIF1 from mouse brain tissues and that is:

Journal of Cerebral Blood Flow and Metabolism, 22:393-403. 2002 by Myriam Bernadin et al. For extraction they cited another paper published by Hayashi et al in 1997..Stroke 28:2039-2044.

I have done some work on nuclear factor proteins in cell culture but that is little bit different from brain tissue itself. I agree with Johnny that the extraction has to be faster so the nuclear proteins do not degrade. Good luck.