An enzymatically active product for use in isomerization of glucose into fructose is provided. The active product comprises an organic polymeric material predominantly comprised of a monovinyl aromatic compound polymer having .beta.-aminopropionamidomethyl group as side chains represented by the formula I: ##STR1## wherein R.sub.1 is selected from H, C(1-6) alkyl and C(2-6) hydroxyalkyl, R.sub.2 is selected from C(1-6) alkyl, C(2-6)hydroxyalkyl, ##STR2## (where X, Z.sub.1 and Z.sub.2 are selected from H and C(1-6) alkyl, and n is from 2 to 6), or R.sub.1 and R.sub.2 form together with the N atom, to which R.sub.1 and R.sub.2 are bonded, a heterocylic structure of the formula: ##STR3## where A is --CH.sub.2 --, --O-- or --NR.sub.6 -- (wherein R.sub.6 is H or C(1-6) alkyl), and R.sub.3, R.sub.4 and R.sub.5 are selected from H and methyl. The organic polymeric material has glucose isomerase immobilized with the .beta.-aminopropionamidomethyl group side chain of the organic polymeric material.