I have purified the E. coli enzyme BirA using the Ni-NTA column purification method and eluted the protein in 350 mM imidazole, 20mM Tris (pH 8), 150mM NaCl solution. what should be the storage temperature and buffer composition?
In general, you can dialyze the eluted protein sample into a buffer without imidazole, and quick freeze small aliquots of the purified protein in liquid nitrogen and store them at -80C degrees.
As suggested by Mr. Xiao, first you should remove the imidazole from your purified protein by buffer exchange method. you can use pH 8 of phosphate buffer to remove imidazole from your sample and then you can store it at -80C degree in small aliquots.
First is to remove imidazole by dialysing the protein sample against the elution buffer - imidazole and then add 10% glycerol to the protein sample, flash freeze in liquid nitrogen and store at -80 C.