Arginase liver

Figure 16.4 Dinuclear Mn centre of rat liver arginase. (From Ash, 2004. Copyright 2004, the American Society for Nutritional Science.)...

Cleavage of arginine to ornithine and urea Arginase cleaves arginine to ornithine and urea, and occurs almost exclusively in the liver. Thus, whereas other tissues, such as the kidney, can synthesize arginine by these reactions, only the liver can cleave arginine and, thereby, synthesize urea. 

Arginine is cleaved by arginase to produce ornithine. [Note This reaction occurs primarily in the liver as part of the urea cycle (9ee p. 253).] Ornithine is subsequently converted to a-ketoglutarate. 

The complete urea cycle as it occurs in the mammalian liver requires five enzymes Argininosuccinate synthase, arginase, and argininosuccinate lyase (which function in the cytosol), and ornithine transcarbamoylase, and carbamoyl phosphate synthase (which function in the mitochondria). Additional specific transport proteins are required for the mitochondrial uptake of L-ornithine, NH3, and HC03 and for the release of L-citrulline. 

Would you anticipate elevated arginase activity in the liver of an untreated diabetic animal Why or why not ... 

The 2.8 A resolution crystal structure of the arginase from the thermophilic bacterium Bacillus caldevelox [112] reveals a hexameric structure with at least one Mn2+ bound per subunit. The 2.1 A resolution structure of rat liver arginase, reported recently [81], reveals it to be trimeric, with the overall fold of the arginase monomer belonging to the a/p protein class. The Mn"Mnn aggregate, shown in Figure 24, is found at the bottom of a 15 A active-site cleft. 

Although mammalian liver arginases can be activated by Co2+, Ni2+, Fe2+, and Cd2+, only Mn2+ is considered [114] to be the physiological activator. Mn2+ is specifically required to activate the arginases from Neurospora crassa [115], Rhodobacter capsulatus [116], and the Agrobacterium TiC58 plasmid. This selectivity is attributed to the unique ability of Mn to orient the bridging water molecule properly for catalysis [81,117],... 

Arginase Argininemia ARG1 6q23 Liver, RBC Citrulline T ... 

Examples of typical enzyme names are arginase, which acts on arginine, and urease, which acts on urea (Chap. 15). Two atypical common names are pepsin, a digestive tract proteolytic enzyme (EC number 3.4.23.1), and, more exotically, rhodanese (thiosulfate cyanide sulfurtransferase, EC 2.8.1.1), which is in mammalian liver and kidney and catalyzes the removal of cyanide and thiosulfate from the body. In the latter case, it is understandable why the old name has remained in common use. 

Arginase is a hydrolase that is in the liver of urea-producing organisms (ureoteles). It catalyzes the reaction ... 

Enzyme arginase, which is located primarily in the liver and is inhibited by ornithine. 

Arginine can be cleaved by arginase in the liver to form urea and ornithine. Ornithine can be transaminated to glutamate semialdehyde, which can be oxidized to glutamate. 

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