ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Characteristics of immobilized urease onto modified zirconium (IV) oxide via glutaraldehyde: kinetic, stability, and operational stabilities in bioreactors

Özlem Alptekin

Department of Biochemistry, Faculty of Pharmacy, Cukurova University, Adana, Turkey

E-mail: oalptekin@cu.edu.tr

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 K_m value of urease was increased from 2.7 ± 0.1 to 10.2  ± 0.4 mM and the V_max 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.

Graphic abstract

Keywords: Urease; Immobilization; Zirconium (IV) oxide; Operational stability; Bioreactors

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-021-01891-6

Chemical Papers 76 (2) 749–761 (2022)