Arginase catalyzes the hydrolysis of L-arginine into urea in the final step of the urea cycle
. There are two argianse isozymes in mammals. Arginase I functions in the urea cycle in the cytoplasm of the liver. Arginase II, implicated in the regulation of the arginine/ornithine concentrations in the cell, is located in mitochondria of several tissues in the body, with most abundance in the kidney and prostate. Arginase II and nitric oxide synthetase, sharing the common substrate of L-arginine, are coexpressed in smooth muscle tissue in the genitals of both men and women. Inhibition of arginase II was shown to allow normal muscle relaxation and sexual response. Thus, arginase has been implicated as a potential target for treatment of sexual dysfunction in both sexes. Arginase I deficiency
is referred to as hyperargininemia or arginemia
. Symptoms of the disorder
include neurological impairment, dementia
, and retardation of growth. It is characterized by low arginase activity in hepatic cells.
Chemediate provide a sensitive continuous spectrophotometric measurement of enzyme activity using thioarginine is an alternative substrate. It exhibits Km and kcat values of 0.5 mM and 18,000 min−1, respectively, which are similar to physiological substrate arginine. The thiol product of the reaction further reacts with Ellman’s reagent (DTNB) in situ to produce the chromophore of 2-nitro-5-thiobenzoate for detection at 412 nm.