Molecular Characteristics of Rat Liver Arginase

The molecular weight of approximately 1,500-fold purified arginase from rat liver (specific activity = 19,500 µmoles of urea per min at 25° per mg of protein nitrogen) was determined by the method of sedimentation equilibrium to be 118,000. The sedimentation velocity constant is 6.1 S, the diffusion coefficient 5.2 x 10-7 cm2 per sec. Alteration in pH, removal of Mn2+, and replacement of Mn2+ by Co2+ did not yield evidence of a change in molecular size. The partial specific volume (V) was determined by a differential sedimentation equilibrium technique in heavy water. Dissociation of the enzyme in 8 m urea yielded a protein which sedimented in a single boundary and gave one protein band after acrylamide gel electrophoresis. Sedimentation equilibrium analysis of the dissociation compound gave a molecular weight of 30,800, which suggests that rat liver arginase is composed of four subunits. Amino acid analysis has been carried out and the values compared to those of arginases from other species.