Crosslinked polyethylenimine: An enzyme carrier with spacers of various lengths introduced in crosslinking reaction

Polyethylenimine (PEI) reacted with epichlorhydrin to various degrees of crosslinking was further activated with thiophosgene or with succinic anhydride; the carboxyl derivatives obtained were converted to hydrazide derivatives. d-Glucose oxidase (β-d-glucose:oxygen 1-oxidoreductase, EC 1.1.3.4), glucoamylase (exo-1,4-α-d-glucosidase, 1,4-α-d-glucan glucohydrolase, EC 3.2.1.3) and cholinesterase (acetyl-, butyryl-) [acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7), butyryl cholinesterase (acylcholine acylhydrolase, EC 3.1.1.8)] were bound in their native forms to the first two types of carriers, while in the case of the hydrazide derivative of crosslinked PEI this occurred just after periodate oxidation of a glycoenzyme. The PEI derivatives prepared from the crosslinked PEI with the lowest degree of crosslinking, i.e. from that having the longest mean length of the spacer (～ 11.1 Å), revealed the best binding properties towards low-molecular thiols, amino acids and proteins/enzymes. After enzyme coupling, the isothiocyanate derivatives of crosslinked PEI gave preparations with the highest residual activities.