Immobilization of Amyloglucosidase onto Granular Chicken Bone
Amyloglucosidase was immobilized onto granular chicken bone (BIOBONE TM) by noncovalent interactions. The amount of activity bound relative to an equal amount of free enzyme was 13.6+0.4%. The estimated specific activity for amyloglucosidase decreased from 75.3+0.8 to 43.5+9.6 U/mg protein upon immobilization. The Km value of the bone-immobilized enzyme using glycogen as substrate increased from 3.04+0.38 mg/mL (free) to 9.04+l.51 mg/mL (immobilized), but Km showed no change upon immobilization when starches were used as substrates. A decrease in Vmax values occurred upon enzyme immobilization for all substrates, but this largely reflected the percentage of enzyme initially bound to the bone. Immobilization also improved enzyme stability in the presence of various additives (e.g., detergent, KCl, and ethanol) or under low or high pH reaction conditions. Bound amyloglucosidase maintained high activity (greater than 90%) following five cycles of continuous use at moderate (23°C) and high (55°C) temperatures. Data derived from Lineweaver-Burk and Arrhenius plots indicated that substrate and product diffusion limitation were minimal.