Abstract: Cross-linked oxalate decarboxylase aggregates (oxdc-CLEAs) for use as an enzyme preparation to relieve urinary oxalate stone disease were prepared by a carrier-free immobilization method. Crude enzyme solution was obtained from the induced expression of the genetically engineered strain E.coli BL21(DE3)/pET32a/YvrK, and oxalate decarboxylase was separated by adding 30% ethanol with a purification factor of 2.7 and an activity recovery of 91.2%. Cross-linked oxdc-CLEAs were further obtained after 2 h of cold treatment at 4 ℃ in the presence of 0.5 g/L bovine serum albumin (BSA) and 0.06% glutaraldehyde at pH 5, resulting in an activity recovery of 95.4%. Enzymatic characterization showed that cross-linked oxdc-CLEAs had improved tolerance to acid, heat and trypsin degradation when compared to free oxalate decarboxylase.

Key words: oxalate decarboxylase, cross-linked enzyme aggregates, preparation, properties