Arginase

I.U.B.: 3.5.3.1
L-Arginine amidinohydrolase

Arginase catalyzes the following reaction:

The enzyme participates in the Krebs-Henseleit urea cycle. It is most highly concentrated in mammalian liver. Arginase is also present in abundance in mammary glands where the urea cycle is not present: it has been suggested that the ornithine is converted to proline (Yip and Knox 1972). Farron (1973) indicates that arginases of different organs are different proteins and serve different metabolic functions. See also Grazi and Magri (1972) and Grazi et al. (1972) on the ureotelic and uricotelic arginases of chicken liver.

Human arginase has been reported on by: Porembska and Kedra (1975); Reyero and Dorner (1975); Van Elsen and Leroy (1975); Carvajal et al. (1971); Nishibe and Makino (1971a); Azizi et al. (1970). Rat tissue arginases have been studied by Greengard et al. (1970); Hirsch-Kolb et al. (1971); Hosoyama (1972); Yip and Knox (1972); and by Kaysen and Strecker (1973). That from hamster has been studied by North et al. (1971); rabbit liver by Vielle-Breitburd and Orth (1972); and chicken liver by Traniello et al. (1975); Grazi and Magri (1972) and Grazi et al. (1972). O'Malley and Terwilliger (1974) report on arginase from polychaete annelid.

Characteristics of Arginase from Bovine Liver:

Molecular weight: 115,000-120,000 (Harell and Sokolovsky 1972).

Composition: The amino acid content has been reported by Greenberg (1960). According to Harell and Sokolovsky (1972) the enzyme does not split into subunits; it binds 4 atoms of Mn²⁺ which are essential to its activity as well as stability and has a hexose content of 3-5%.

Optimum pH: 10 (Mn²⁺ activated, Greenberg 1960).

Extinction coefficient: = 9.6 (Harell and Sokolovsky 1972).

Activators: Mn²⁺, Ni²⁺, or Co²⁺.

Specificity: Arginase activity requires the free guanidino group and the free carboxyl group of arginine (Greenberg 1960).

Inhibitors: Hg²⁺, Ag²⁺, Zn²⁺.

Stability: Bond (1973) reports that susceptibility of beef liver arginase to proteolytic inactivation is enhanced by increasing activating concentration of Mn²⁺. Cysteine, isoleucine, leucine, valine and alanine protect the enzyme against trypsin inactivation.

The enzyme is highly stable when stored refrigerated as a solution at neutral pH or as a lyophilized powder.