A biologically active preparation of murine recombinant interleukin-1β (mIL-1β) fromEscherichia coli cell lysates contained two forms of mIL-1β with pI 8.7 and pI 8.1, respectively. Treatment with 0.1 M Tris, pH 8.5, at 37°C for 35 h converted the pI 8.7 form to the pI 8.1 form by the selective deamidation of an asparagine residue (Asn149) in the mIL-1β molecule. Deamidated mIL-1β had 3- to 5-fold lower co-mitogenic activity and receptor affinity than the unmodified form.
