Poly(ethylene glycol)-bovine serum albumin hydrogel as a matrix for enzyme immobilization.: In vitro biochemical characterization

Arginase, isolated from beef liver, apyrase and glutaminase, isolated from Escherichia coli, were immobilized during the synthesis of a hydrogel matrix made from poly(ethylene glycol) (PEG) and bovine serum albumin (BSA). After synthesis, a one- to three-fold increase in the K-m values was observed for the enzymes. The apparent K-m were 30 mM of arginine, 6.5 mM of glutamine, and 52 mu M of ATP for immobilized arginase, glutaminase, and apyrase, respectively. In general, immobilization allowed the enzymes to retain most of their initial activity; after incubating for 1 month at 37 degrees C in the presence of the respective substrates, more than 95% of the initial activity was found. The optimal temperatures varied from 40 to 60 degrees C for all enzyme preparations. The immobilized arginase, glutaminase, and apyrase had optimal activity over a larger pH range which was due to the matrix effect. Surface modification of arginase with 5,000 Mw methoxy-PEG increased the stability for up to 24 days (incubated at 37 degrees C) compared to eight days for the native enzyme tested under the same conditions. However, this modification did not affect the stability of glutaminase.