2.3. Immobilization of proteins
PHB nanofibers (5 mg), 150 mg of PHB granules (Goodfellow, Huntingdon, UK), 25 mg of Duolite A568 (Novozymes, Kalundborg, Denmark), or 25 mg of Sipernat D17 (Degussa, Frankfurt, Germany) were suspended 1 mL of protein solutions (0.2−0.3 mg) and incubated overnight at 4°C or for 1 h at 30°C under constant shaking. These supports were recovered by a brief centrifugation step and washed three times with 50 mM TRIS-HCl buffer (pH 8.0). The amount of protein adsorbed to the support was calculated by measuring the protein concentration in the buffer solution sampled before and after the immobilization procedures.