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CHARACTERIZATION OF ARGINASE FROM THE LIVER OF MANGO TILAPIA (Sarotherodongalilaeus)

ABSTRACT

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.

CHAPTER ONE

INTRODUCTION

BACKGROUND OF THE STUDY

Arginase is a vital enzyme that plays a crucial role in the urea cycle, which is responsible for the elimination of nitrogenous waste in organisms. It catalyzes the hydrolysis of arginine to ornithine and urea, contributing to the regulation of arginine metabolism and the overall balance of nitrogen in various organisms. Understanding the characteristics and properties of arginase enzymes from different species is essential for elucidating their physiological roles and exploring potential applications in diverse fields.

The Mango Tilapia (Sarotherodon galilaeus) is a freshwater fish species widely distributed in Africa and known for its economic and nutritional importance. It inhabits various freshwater environments, including rivers, lakes, and swamps, and has adapted to different ecological conditions. The liver is a metabolically active organ that plays a crucial role in the detoxification and regulation of various biochemical processes, including nitrogen metabolism.

Despite the economic and ecological importance of Mango Tilapia, limited information is available regarding the characterization of enzymes involved in nitrogen metabolism, such as arginase, in this species. Characterizing arginase from the liver of Mango Tilapia can provide insights into its enzymatic properties, substrate specificity, and potential regulatory mechanisms.

Characterization studies on arginase have been conducted in various organisms, including mammals, birds, and other fish species, revealing differences in enzymatic properties, tissue distribution, and regulatory mechanisms. These studies have highlighted the significance of understanding the functional diversity of arginase enzymes across species.

The present study aims to characterize arginase obtained from the liver of Mango Tilapia, focusing on its enzymatic activity, optimal conditions for activity, kinetic parameters, and the effect of metal ions and inhibitors on its function. By elucidating the properties of arginase in Mango Tilapia, this research will contribute to expanding our knowledge of arginine metabolism in this species and its potential implications in aquaculture, health, and biotechnology.