PREPARATION AND PROPERTIES OF GLUCOSE-ISOMERASE IMMOBILIZED ON INDION48-R

Partially purified glucose isomerase from Streptomyces thermonitrifica ns when coupled to glutaraldehyde-activated Indion 48-R, retained 30-4 0% activity of the soluble enzyme. However, an approximately twofold i ncrease in the activity could be achieved by binding the enzyme in the presence of glucose. Binding the enzyme to matrices presaturated with either glucose or fructose and influence of lysine modification on th e activity of the soluble enzyme revealed that the comparatively low a ctivity observed in case of the enzyme bound in the absence of substra te is the result of the nonspecific binding of either substrate or pro duct to the matrix. Immobilization did not affect the pH and temperatu re optima of the enzyme, but it lowered the temperature stability. Imm obilization resulted in a marginal increase in the K(m) and a threefol d decrease in the V(max). Substrate concentrations as high as 36% gluc ose could be converted to 18.5% fructose in 5 h, at pH 7.0 and 70-degr ees-C. The bound enzyme, however, showed inferior stability to repeate d use and lost approx 40% of its initial activity after five cycles of use. Indion 48-R bound glucose isomerase could be stored, in wet stat e, for 30 d without any apparent loss in its initial activity.