Characteristics of immobilized urease onto modified zirconium (IV) oxide via glutaraldehyde: kinetic, stability, and operational stabilities in bioreactors
Received: 24 April 2021 Accepted: 21 September 2021
Abstract:
This study aimed to obtain an efficient immobilized urease covalently immobilized onto modified zirconium (IV) oxide (ZrO2) that could serve in a dialysate regeneration system. For the first time, the characteristics of modified ZrO2 and immobilized urease preparations were studied in detail. The operational stabilities of urease in batch and continuous flow-type reactors were also compared. ZrO2 was sequentially modified with Piranha, 3-aminopropyl triethoxysilane, and glutaraldehyde (GA) followed by urease immobilization. The surface area of the carrier was increased by 29% after Piranha treatment. The bound urease onto modified ZrO2 was 3.9 mg g carrier−1. Optimum pH and temperature of free and immobilized ureases were found as 6.5 and 50 °C, and 7.0 and 60 °C, respectively. Following immobilization, the Km value of urease was increased from 2.7 ± 0.1 to 10.2 ± 0.4 mM and the Vmax value decreased from 51.6 ± 2.0 to 0.16 ± 0.02 U mg protein−1. The immobilized urease was 62, 35, and 46 fold more stable than the free urease at 50, 60, and 70 °C, respectively. It showed 90 and 58% of its initial activity at 4 °C and room temperature at the end of 12 days, respectively. The amount of removed urea was found to be 0.22 mg in a batch-type reactor and 0.39 mg in a continuous flow-type reactor at the end of 60 min. The immobilized urease onto ZrO2 has superior potential to use in artificial kidney machines due to significant contribution to reducing device weight.