Immobilization of γ-glutamyltranspeptidase on silylated mesoporous TiO2 whiskers

The surface of mesoporous TiO2 whiskers (MTw) was chemically modified with 3-aminopropyltriethoxysilane (APTES). The point of zero charge (pzc) of MTw and the modified material (MTwA) was 5.3 and 6.8, respectively. MTw and MTwA were then used as carrier to immobilize γ-glutamyltranspeptidase (GGT) from Bacillus subtilis (B. subtilis). Our results indicated that the loading capacity of MTwA for GTT was significantly superior to that of MTw. Although the optimum temperature and thermal stability of MTwA-GGT were slightly lower than those of MTw-GGT, its pH stability was greatly improved compared with either free enzyme or MTw-GGT. The affinity constant (K m ) of MTwA-GGT to γ-glutamyl-p-nitroanilide (GpNA) was 0.889 mM, higher than that of free enzyme but lower than that of MTw-GGT. In addition, MTwA-GGT displayed a good operational stability.