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 dimethylsu berimidate was surveyed. In the enzymes investigated, a moderate incre ase of thermostability in glucose oxidase and invertase, and prominent increase in lactate dehydrogenase, alcohol dehydrogenase and ascorbat e oxidase were observed. The increase of thermostability by amidinatio n was suggesting the synergism of the enhancement of intersubunit salt bridges and the conformational stabilization by intra- and intermolec ular 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 thermostabilit y was observed for catalase, ascorbate oxidase, lactate dehydrogenase and alcohol dehydrogenase and a prominent increase was observed for di aphorase, alpha-chymotripsin, glucose oxidase and invertase. Enhanced thermostabilities of enzymes may be attributed to the mild procedure o f the preparation of enzyme-dextran-conjugate, the introduction of pol yol structure on or around the surface of enzyme molecule and the intr amolecular cross-linking with hexamethylenediamine.