Exploring the catalytic potential of watermelon urease: Purification, biochemical characterization, and heavy metal precipitation

Abstract

Bioactive urease from watermelon (Citrullus lanatus) seeds was purified using acetone fractionation, anion-exchange, and size-exclusion chromatography, achieving a 121-fold increase and specific activity of 3216 U/mg. The enzyme appeared as a single band on native and SDS-PAGE, with a molecular mass of 480 ± 10 kDa and subunit mass of 80 ± 10 kDa, indicating six identical subunits. Atomic absorption spectroscopy revealed 1.46 nickel ions per subunit. Watermelon urease exhibited serological similarities with jack bean and pigeon pea ureases, an optimal pH of 7.3, an activation energy of 3 kcal/mol, V_max of 3571 μmol/min/mg, and K_m of 0.16 mM. The enzyme displayed biphasic thermal and pH inactivation kinetics, a strong preference for urea, and a half-life of 70 days with 1 mM DTT. This study highlights watermelon urease's role in bioremediation by facilitating the precipitation of heavy metals as stable carbonates, promoting environmental sustainability.

Keywords: Citrullus lanatus seeds; Heavy metals precipitation; Urease.