Thermostabilization of Modified Enzymes by Amidination with Dimethylsuberimidate or by Combination of Enzyme-dextran Conjugate with Hexamethylenediamine

The thermostabilization of some enzymes by amidination with dimethylsuberimidate was surveyed. In the enzymes investigated, a moderate increase of thermostability in glucose oxidase and invertase, and prominent increase in lactate dehydrogenase, alcohol dehydrogenase and ascorbate oxidase were observed. The increase of thermostability by amidination was suggesting the synergism of the enhancement of intersubunit salt bridges and the conformational stabilization by intraand intermolecular cross-linking. The coupling of oxidized dextran with periodate on the surface of the enzyme molecule (enzyme-dextran-conjugate) and the subsequent cross-linking with hexamethylenediamine were also proposed to enhance the thermostability. A moderate increase of thermostability was observed for catalase, ascorbate oxidase, lactate dehydrogenase and alcohol dehydrogenase and a prominent increase was observed for diaphorase, (Y chymotripsin, glucose oxidase and invertase. Enhanced thermostabilities of enzymes may be attributed to the mild procedure of the preparation of enzyme-dextran-conjugate, the introduction of polyol structure on or around the surface of enzyme molecule and the intramolecular cross-linking with hexamethylenediamine.