Protein purification
For purification of adenosine deaminase, 5 ml of E. coli BL21
(DE3) carrying pET-ada from overnight grown culture in LB supplemented
with 60 lg/ml ampicillin was transferred to one liter of LB
plus ampicillin. The culture was allowed to grow to an OD600 nm of
0.5 and induced by addition of lactose at a final concentration of
1 mM, since lactose had been shown to be as an effective inducer
as IPTG [11]. After five additional hours of growth, cells were harvested
by centrifugation at 10,000g at 4 C, suspended in lysis buffer
[20 mM Tris–HCl (pH 8.0), 50 mM KCl, 1 mM EDTA, 0.5% Tween