The purification and characterization of human kidney l-arginine:Glycine amidinotransferase

Human kidney l-arginine:glycine amidinotransferase (transamidinase) has been purified to a homogeneous state as defined by native and sodium dodecyl sulfate gel electrophoresis and by ultracentrifugation (sedimentation equilibrium) experiments. The four steps in the isolation procedure were chromatography with DEAE-cellulose, gel filtration with Sephadex G-150, chromatography with phenyl Sepharose, and high-pressure liquid chromatography with hydroxylapatite. The final product represented a 90-fold purification of the enzyme. Human kidney transamidinase is a dimer with a molecular mass of 89,000 Da and subunit masses of 44,000 Da. The K_m for arginine and glycine were both 2.5 mm and the V_max was 0.5 μmol ornithine/min/mg protein. The ultraviolet absorption spectrum, specific activity, and isoelectric points were determined for human kidney transamidinase. Multiple forms of the enzyme were obtained by isoelectric focusing. Human kidney transamidinase cross-reacted with polyclonal antibodies raised to rat kidney transamidinase. All of the properties of human kidney transamidinase that we have examined were similar to those of rat kidney transamidinase. A close evolutionary relationship between the rat and human kidney transamidinase is suggested.