Characterization Of Arginase From The Liver Of Mango Tilapia (Sarotherodongalilaeus)

Arginase is a detoxifying enzyme that catalyses the hydrolysis of arginine into ornithine and urea, the last step of urea cycle- a process through which the body disposes off harmful ammonia. This research was carried out to determine the characteristics of liver arginase of mango tilapia (Sarotherodongalilaeus) in Opa river, Osun state.

The enzyme ‘arginase’ was isolated from the liver of mango tilapia through the process of homogenization and centrifugation which was done at 4000rev/min.The protein concentration was determined using Bradford method and the arginase assay was determined by Kaysen and Strecker method.

The kinetic study shows that mango tilapia of liver arginase has a Km value of 0.2M and a Vmax value of 166.7µmol/ml/min. The effect of temperature on arginase activity was tested and the optimum temperature for mango tilapia liver arginase is 50°C at activity of 63.44µmol/ml/min. The effect of pH was also investigated and optimum pH is 8.0 at activity of 165.1µmol/ml/min. Inhibition study was also carried out and it was observed that calcium (51.4±1.13) and zinc (51.5±4.27) strongly inhibit arginase while mercury, magnesium and sodium have little or no inhibitory effect on arginase. Also from the result, it can be deduce that citrate (20.8±4.67) and glutathione (28.6±2.53) and ethylenediamineacetic acid (EDTA) slightly inhibit arginase while urea has les inhibitory effect on arginase. The result for the effect of amino acids on enzyme activity shows that liver arginase of mango tilapia to be in this order: arginine > valine> aspartate > cysteine > lysine with residual activity of 107.2%, 86.6%, 73.4%, 62.1% and 58.7% respectively.

Mango tilapia liver arginase belongs to the ureotelic class of arginases according to Mora J et al classification (1965). It has a Km value of 0.2M and aVmax value of 166.7µmol/ml/min.