Arginase catalyzes the conversion of arginine to urea and ornithine in the liver of ureotelic animals. Higher activity of this enzyme is found in tumors as well as in the sera of patients with hepatic diseases. We have developed a simple colorimetric method for its determination. This is based on the determination of residual arginine, after its conversion with p-nitrophenyl glyoxal (PNPG) at pH 9.0 in the presence of sodium ascorbate. The reaction product obeys Beer's law in the range of 0.01-0.20 mmol/L arginine with an arginine-equivaient molar extinction coefficient of 0.65 x 104 M -1 cm -1. The decrease in absorbance in the presence of arginase correlates with the enzyme activity. Color development as well as termination of enzyme activity is achieved by addition of a single reagent, thereby obviating the use of many chemicals necessary in other methods. The sensitivity of this method is equivalent to those of currently available procedures but has the added advantages of greater convenience.
sorption of arginine and ornithine plus urea at 205-215 nm (21). A sensitive and rapid assay for arginase that also measures urea uses guanidino-Z4C arginine as substrate ( 22).
Most of these methods are tedious, inconvenient, and involve multiple technical manipulations. This paper describes the development of a rapid procedure for the direct determination of arginase based on the colorimetric determination of arginine remaining after its hydrolysis by arginase, using the single reagent p-nitrophenyl glyoxal (PNPG).