Purification and characterization of buffalo liver L-arginase and its kinetic properties with dihydropyrimidine and metal ions.

Arginase (L-arginine amidinohydrolase, EC.3.5.3.1) from animal tissues such as, liver and kidney has been partially characterized by many researchers. In this study, we purified arginase to homogeneity from buffalo liver with about ~2857 purification fold and a 20% recovery by chromatographic and spectroscopic analysis were obtained. The molecular mass determined by gel filtration and SDS-PAGE was found to be 118 kDa and 47 kDa, respectively. The optimal pH and temperature of the arginase was 9.5 and 40°C, respectively. Kinetic parameters (Km and Vmax) showed activation of arginase in the reaction medium with decrease in Km (7.14, 5.26, 4.0 and control 3.22 mM) and Vmax (0.05, 0.035, 0.027 and control 0.021 mg/mL/min), while co-factor activity of arginase was optimized using metal ions like Mn2+ and Mg2+ at 2 mM, which revealed an increase in Vmax values (0.011, 0.013, 0.015 and control 0.010 mg/mL/min) and a decrease in Km values (2.22, 2.12, 1.88 and control 1.66 mM). The kinetic data suggested that the arginase activity is enhanced in the presence of dihydropyrimidine derivative and metal ions, indicating essential mode of activation.

Arginase isoforms in frog and lizard tissues.

Isoforms of arginase in the liver and kidney tissues of the ureotelic frog (Rana tigerina) and uricotelic lizard (Calotes versicolor) were fractionated by DEAE-cellulose chromatography (pH 8.3). Four molecular forms, designated as A’1, A2, A3 and A4 based on the KCl concentration required for their elution from the ion-exchange column, were detected in lizard liver, while only two forms were found in lizard kidney (A3 and A4) and frog liver and kidney (A2 and A3). No major differences were found in the pH optimum, substrate affinity and molecular weight of the isoenzymes. The isoforms in lizard tissues were either totally unaffected or only partially immunoprecipitated by antibodies raised against rat liver and beef liver arginases, but those in frog tissues were significantly activated by the two antibodies. While the physiological importance of the presence of four isoforms in lizard liver remains enigmatic, different sets of isoenzymes were present in the liver of the two ureotelic vertebrates, rat and frog. Hence, it appeared that a given mode of nitrotelism was not associated with a specific set of isoenzymes. Also, the data were not consistent with the generally held view that a basic isoform of arginase served as a component of the urea cycle in liver and a neutral/slightly acidic form functions in the synthesis of proline, glutamate and polyamines in extra-hepatic tissues. The isoforms appeared to show considerable functional overlap.