Rat recombinant calbindin D-9k (recombinant) produced in Escherichia Coli

Purification 
E. coli containing a His6-fusion protein were disrupted in a buffer containing 6M GuHCl/0.1 
M NaH2PO4. After a low speed centrifugation to remove cell debris, the supernatant was 
applied to the charged NTA resin column, equilibrated in disruption buffer, before the column 
being washed with the same buffer. Afterwards, the column was washed and the HIS6-
fusion proteins eluted by decreasing the pH of the eluent (8 M Urea /0.1 M Na2HPO4) in a 
stepwise manner (pH 6.3 / 5.9 / 4 / 2). The protein was dialysed against phosphate buffered 
saline, 0.1 M, pH 7.3 (PBS