Some biochemical properties of arginase in cattle rumen tissue

105 6. SUMMARY The aim of this study was to establish some properties of rumen tissue arginase in cattle slaughtered at Elet abattoir in Elazığ, using Thiosemicarbazide Diacetylmonoxime Urea method as the criterion. Some biochemical properties of purified and non-purified rumen tissue arginase were compared. It was found that pre-incubation temperature (60° C) of arginase and Km (4mM) to its substrate, L-arginine, did not change before and after purification. While pre-incubation period was 10 min and optimal pH 9.7 before purification, pre-incubation period was found to be 5 min and optimal pH 10 after purification. Purified enzyme achieved its highest activity at 2mM MnCI2 concentration, whereas non-purified enzyme gave the highest activity at 1mM MnCI2 concentration. Consequently, it was determined that Mn++ cations and pre-incubation at 60°C were essential for the activation of the enzyme. L-amino acids, such as valine, leucine, isoleucine, ornithine, cysteine, proline, lysine inhibited the enzyme activity noncompetitively. On the other hand, histidine and hydroxyproline were not determined to have any inhibitory effect on the enzyme activity. Among guanidino compounds, canavanine, agmatine and guanidine inhibited the enzyme noncompetitively; 0.35mM canavanine and 12mM guanidine caused 100% inhibition in the enzyme's activity. The noncompetitively inhibition of rumen tissue arginase by p-CMBA and NEM indicates that functional -SH groups may be present in the active centre of this enzyme.