The effect of pH on the solubility of recombinant HP-NAP upon
lysis. A, E. coli BL21(DE3) expressing HP-NAP was suspended in ice-cold Tris–HCl buffer at the indicated pH ranging from 7.0 to 9.5. Cells were then disrupted by sonication as described in Methods. Whole cell lysates (W) were centrifuged to separate soluble fractions (S) and insoluble pellets (I). The proteins were analyzed by SDS-PAGE. Molecular weights (M) in kDa are indicated at the side of the gels. B, The percentage of solubility of recombinant HP-NAP in the whole cell lysate at each pH was calculated from the intensity of HP-NAP band on SDS gels for the soluble fraction (S) divided by that for the whole cell lysate (W). Data were represented as the mean ± S.D. of at least two experiments.