Arginases

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 

The Photosynthetic Oxygen-evolving Center (OEC) of Photosystem II (PSIl) 

---

Argentite [1332-04-3] Argentodi thiosulfate Argentotri thiosulfate Arginase... 

Mn-+ K+ Ni " Arginase Pyruvate kinase (also requires Mg ) U rease Tetrahydrofolate (THF) Other one-carbon groups Thymidylate synthase... 

L-Arginine Arginase + Urease (double reaction) nh3, co2 Tris pH 7 NHj-airgap ... 

Hyperargininemia. This defect is characterized by elevated blood and cerebrospinal fluid arginine levels, low erythrocyte levels of arginase (reaction 5, Figure 29-9), and a urinary amino acid pattern resembling that of lysine-cystinuria. This pattern may reflect competition by arginine with lysine and cystine for reabsorption in the renal tubule. A low-protein diet lowers plasma ammonia levels and abolishes lysine-cystinuria. 

Iyer R et al The human arginases and arginase deficiency. J Inherit Metab Dis 1998 21 86. 

Arginase, activity of polyethylene glycol modified enzymes, 98 -99 Aromatic monomers, limited biocompatibility, 155 Asparaginase, activity of polyethylene glycol modified enzymes, 98-99 Autacoids, inactivation during systemic delivery, 266-267... 

Argininosuccinate lyase (AL) (Fig. 40-5 reaction 4) cleaves argininosuccinate to form fumarate, which is oxidized in the tricarboxylic acid cycle, and arginine, which is hydrolyzed to urea and ornithine via hepatic arginase. Both AL and arginase are induced by starvation, dibutyryl cyclic-AMP and corticosteroids. 

The importance of manganese for bacteria, such as that of Ni and to a lesser extent Co, as we saw in the last chapter, is considerable. Of course, as we will see shortly, it is also important in the tetranuclear Mn cluster that is involved in oxygen production in photosynthetic plants, algae and cyanobacteria, as well as in a number of mammalian enzymes such as arginase and mitochondrial superoxide dismutase. Most of manganese biochemistry can be explained on the one hand by its redox activity, and on the other by its analogy to Mg2+ (reviewed in Yocum and Pecoraro, 1999). 

We begin this overview of manganese biochemistry with a brief account of its role in the detoxification of free radicals, before considering the function of a dinuclear Mn(II) active site in the important eukaryotic urea cycle enzyme arginase. We then pass in review a few microbial Mn-containing enzymes involved in intermediary metabolism, and conclude with the very exciting recent results on the structure and function of the catalytic manganese cluster involved in the photosynthetic oxidation of water. 

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

Nau WM, Ghale G, Hennig A et al (2009) Substrate-selective supramolecular tandem assays monitoring enzyme inhibition of arginase and diamine oxidase by fluorescent dye displacement from calixarene and cucurbituril macrocycles. J Am Chem Soc 131 11558-11570... 

Arginase 3.5.3.1 L-Arginine L-Ornithine/urea Urea-selective electrode... 

---