[Comparison of chemical and thermal stability of soluble and immobilized alpha-amylases from B. licheniformis and A. oryzae].

alpha-Amylases from B. licheniformis and A. oryzae, which differ in their thermal stability, were studied with respect to their resistance to chemical denaturants as guanidine hydrochloride, urea, aliphatic alcohols, and formaldehyde. Moreover, the thermal and chemical stabilities of both enzymes were compared after their covalent binding to gamma-aminopropyl silica. The thermolabile alpha-amylase (A. oryzae) as well as the thermostable alpha-amylase (B. licheniformis) are remarkably stabilized by immobilization. Therefore, the high thermal resistance of the thermophilic enzyme may be further increased. Soluble and immobilized alpha-amylases from B. licheniformis are more resistant to guanidine hydrochloride, urea, methanol, ethanol, propranol, and t-butanol than the alpha-amylases from A. oryzae. Obviously, the high intrinsic stability of the thermophilic enzyme is also valid for chemical denaturation. An exception is given by the effect of formaldehyde, which may result in chemical modifications of the protein molecule. Enzymes from B. licheniformis are more sensitive against formaldehyde than those from A. oryzae. As in thermal inactivation, immobilization protects alpha-amylase from A. oryzae against denaturation by guanidine hydrochloride and urea, but fails in the denaturation by alcohols. Therefore, stabilizing effects in immobilized enzymes are dependent on the kind of denaturant.