X-Arg dipeptidase

This chapter describes the structural chemistry and the biological aspects of X-Arg dipeptidase. Enzyme activity was determined following incubation of substrate and enzyme in a Tris–HCl buffer, pH 7.0. After the termination of the reaction with 10% trichloracetic acid, released amino acids were measured with an amino acid analyzer. The enzyme generally hydrolyzed dipeptides in which a basic amino acid was present at C-terminus. The preparation method involves a 62-fold purification from the supernatant of a homogenate of 10 kg of hog kidney that was achieved by ammonium sulfate and acetone fractionation and hydroxyapatite chromatography. In the initial step, the enzyme precipitates at 35% ammonium sulfate saturation and is solubilized in a buffer containing 0.4% sodium deoxycholate. The chapter discusses that this enzyme is widely distributed. In the rat, the highest activity is present in skeletal muscle; whereas in the rabbit, the highest activity is present in the kidney. It is possible that the enzyme plays a wider role than hydrolysis of N^α-(γ-aminobutyryl) lysine, perhaps acting in the general hydrolysis of dipeptides containing C-terminal lysine or arginine.