Exuberant Immobilization of Urease on an Inorganic SiO₂ Support Enhances the Enzymatic Activities by 3-fold for Perennial Utilization

Abstract

Urease has been covalently immobilized on a 3-D networking silica gel (SG) using dimethyldichlorosilane (DMDCS) as second generation silane coupling reagent and m-nitroaniline as linker component in a robust methodology and subsequently characterized as [{Si(OSi)₄(H₂O)_0.05}_205.2] _n=4{OSi(CH₃)₂-NH-C₆H₄-N═N-urease}·282.5H₂O (molecular mass 263 445 g or 263.4 kDa). Selective coupling of tyrosine residue with an identifiable m-nitroaniline modified SG unit prevents enzyme-enzyme cross-linking leading to enhancement of enzymatic activity. The material worked at room temperature and its activity (luminescent and ammonia releasing efficiency) was enhanced by 3-fold (for both synthetic and real sample) compared to native enzyme values at neutral pH. Up to 30 days and 30 cycles, this 3-fold activity remains as such but reduces gradually to native enzyme level after 60 days and 60 cycles of reuse.