Hydrolysis arginase catalyzed

Ammonia is highly toxic to animal tissues. In the urea cycle, ornithine combines with ammonia, in the form of carbamoyl phosphate, to form citrulline. A second amino group is transferred to citrulline from aspartate to form arginine—the immediate precursor of urea. Arginase catalyzes hydrolysis of arginine to urea and ornithine thus ornithine is regenerated in each turn of the cycle. 

Fig. 5-4 Arginase-catalyzed hydrolysis of arginine yields ornithine and urea.

Proclavaminate amidino hydrolase (PAH) is one of a number of enzymes that are Mn activated and whose amino acid sequence shows strong homology with arginase. PAH catalyzes the hydrolysis of a guanidino group to give proclavaminate and urea (Equation (8)) ... 

A good comparison of rapid reversible and slow-binding inhibition can be found in a recent study on the inhibition of arginase, an enzyme that catalyzes the hydrolysis of L-arginine to yield L-omithine and urea (Equation 17.31). 

The seed canavanine is rapidly metabolized on germination to canaline and urea [Eq. (1), Fig. 7] by the enzyme arginase which is able to catalyze the hydrolysis of both arginine and canavanine. Urea is further hydrolyzed to ammonia and CO2, the N is presumably utilized for protein amino acid biosynthesis (Rosenthal, 1970 Whiteside and Thurman, 1971). An analysis of a large number of canavanine-containing legumes showed that there was a correlation between canavanine content and urease activity (Rosenthal, 1974). There is limited evidence that canaline is further broken down to homoserine and ammonia. 

These enzymes catalyze the hydrolysis of L-arginine to form L-ornithine and urea. Mammalian arginases have been divided into classes I and II as a function of their location arginase I is predominantly found in the liver whereas arginase II is located in non-hepatic tissues and functions primarily in L-arginine homeostasis [110]. The crystal structure of rat arginase I has shown the active site to be composed of a Mn binuclear center. The Mn(II) and Mn(II)g ions which are... 

Arginase. Urea is formed by the hydrolysis of arginine catalyzed by the enzyme arginase, which was demonstrated in liver in 1904 by Kossel and Dakin (V). A 400-fold purification from horse liver gave a prepara tion that appears to be essentially homogeneous. Arginase requires a... 

STEP 4 OF FIGURE 20.5 ARGININE HYDROLYSIS The final step to complete the urea cycle is hydrolysis of arginine to give ornithine and urea. The reaction is catalyzed by the Mn " -containing enzyme arginase and occurs by addition of H2O to the C=N" " bond, followed by proton transfer and elimination of ornithine from the tetrahedral intermediate. 

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