An L-ornithine high producing strain Bacillus thuringiensis SK20.001 was screened by our laboratory. An intracellular arginase used to biosynthesize L-ornithine from the strain was purified and characterized. The final specific arginase activity was 589.2 units/mg, with 70.1 fold enrichment and 22.4% recovery. The molecular weight of the enzyme was approximately 33,000 Da as evaluated by SOS-PAGE and 191,000 Da as determined by gel filtration. The enzyme had an optimum pH of 10.0 and an optimum temperature of 40 degrees C. It was stable from pH 8.0-12.0 and <50 degrees C without Mn2+. The presence of Mn2+ and Ni2+ had strong effects on the enzyme activity, and Mn2+ significantly increased the thermal stability of the enzyme. The arginase was slightly inhibited by Ca2+, Fe2+ and Zn2+. Trp, Asp, Glu, Tyr, and Arg residues were directly involved in the arginase activity evaluated by chemical modifications. The K-m and V-max for L-arginine were estimated to be 15.6 mM and 538.9 mu mol/min/mg. The biosynthesis yield of L-ornithine was 72.7 g/L with the enzyme. (C) 2013 Elsevier Ltd. All rights reserved.