Stability of native and cross-linked crystalline glucose isomerase

Stabilities of native and cross-linked crystalline forms of Streptomyces ru biginosus glucose isomerase were compared in buffer and in 45% glucose/fruc tose solutions. The cross-linked crystalline form of the enzyme was more st able in this presence of substrate while in a buffer solution the native en zyme was more stable. Inactivation of native enzyme in buffer did not obey first-order kinetics but proceeded with a rapid first phase followed by a s table phase. This stabilization is interpreted to be a result of a conforma tional change in the protein structure. Inactivation of the native enzyme i n buffer was directly related to protein precipitation. In the presence of high substrate concentration, the inactivation was related to browning reac tions between the enzyme and the reactive sugar, resulting in soluble sugar -protein complexes. (C) 1999 John Wiley & Sons, Inc.