L Ornithine

Manometric determiaation of L-lysiae, L-argioine, L-leuciae, L-ornithine, L-tyrosiae, L-histidine, L-glutamic acid, and L-aspartic acid has been reviewed (136). This method depends on the measurement of the carbon dioxide released by the T.-amino acid decarboxylase which is specific to each amino acid. 

L-Ornithine transcarbamoylase catalyzes transfer of the carbamoyl group of carbamoyl phosphate to ornithine, forming citrulline and orthophosphate (reaction 2, Figure 29-9). While the reaction occurs in the mitochondrial matrix, both the formation of ornithine and the subsequent metabolism of citmlline take place in the cytosol. Entry of ornithine into mitochondria... 

Figure 31-4. Conversion of spermidine to spermine. Spermidine formed from putrescine (decarboxylated L-ornithine) by transfer of a propylamine moiety from...

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

This enzyme [EC 1.5.1.24], also referred to as A -(1-l-carboxyethyl)-L-ornithine NADP+ oxidoreductase, reversibly catalyzes the reaction of ornithine with pyruvate and NADPH to produce A -(l-carboxyethyl)ornithine, NADP+, and water. Lysine can also serve as a substrate, acting on A , albeit not as effectively as ornithine. 

This enzyme [EC 2.3.1.35], also known as ornithine ace-tyltransferase, and ornithine transacetylase, catalyzes the reversible reaction of A -acetyl-L-ornithine with L-gluta-mate to produce L-ornithine and A-acetyl-L-glutamate. This protein also exhibits a low hydrolysis activity (about 1% of that of the transferase activity) of iV -acetyl-L-ornithine to yield acetate and L-ornithine. This enzyme is not identical with A-acetylglutamate synthase [EC 2.3.1.1]. 

This enzyme [EC 2.1.4.1], also known as L-arginine gly-cine amidinotransferase, catalyzes the reaction of L-argi-nine with glycine to produce L-ornithine and guanidi-noacetate. Canavanine can serve as the substrate instead of arginine. 

This enzyme [EC 1.5.1.19], also known as D-nopaline synthase, catalyzes the reaction of Al -(D-l,3-dicarboxy-propyl)-L-arginme with NADP+ and water to produce L-arginine, NADPH, and a-ketoglutarate (or, 2-oxoglu-tarate). In the reverse direction, the enzyme catalyzes the formation of D-nopaline from L-arginine as well as D-ornaline from L-ornithine. 

This enzyme [EC 1.5.1.11], also known as D-octopine synthase, catalyzes the reversible reaction of A -(d-1-carboxyethyl)-L-arginine with NAD+ and water to produce L-arginine, pyruvate, and NADH. The enzyme, in the reverse direction, will also act on L-ornithine, L-ly-sine, and L-histidine. 

This pyridoxal-phosphate-dependent enzyme [EC 4.1.1.17] catalyzes the conversion of L-ornithine to pu-trescine and carbon dioxide. 

Ferrichrome was the first siderophore to be isolated and characterized from the fungi Ustilago sphaerogena in 1952. It is a cyclic hexapeptide with the sequence cycto[(Gly)3-(Al -acetyl-Af -hydroxy-L-ornithine)3] (1) . The biologically active ferrichromes form iron(ni) complexes with a left-handed A-cis helical twist. 

Coprogen is a hnear trihydroxamate produced by Penicillium species and Neurospora crassa and was first isolated and characterized by Hesseltine and coworkers . Coprogens are predominantly produced by fungi species and frequently several coprogens are produced by the same species. Coprogen is composed of Af -acyl-A -hydroxy-L-ornithine, anhydromevalonic acid and acetic acid. 

True alkaloids derive from amino acid and they share a heterocyclic ring with nitrogen. These alkaloids are highly reactive substances with biological activity even in low doses. All true alkaloids have a bitter taste and appear as a white solid, with the exception of nicotine which has a brown liquid. True alkaloids form water-soluble salts. Moreover, most of them are well-defined crystalline substances which unite with acids to form salts. True alkaloids may occur in plants (1) in the free state, (2) as salts and (3) as N-oxides. These alkaloids occur in a limited number of species and families, and are those compounds in which decarboxylated amino acids are condensed with a non-nitrogenous structural moiety. The primary precursors of true alkaloids are such amino acids as L-ornithine, L-lysine, L-phenylalanine/L-tyrosine, L-tryptophan and L-histidine . Examples of true alkaloids include such biologically active alkaloids as cocaine, quinine, dopamine, morphine and usambarensine (Figure 4). A fuller list of examples appears in Table 1. 

True alkaloids L-ornithine Pyrrohdine alkaloids Pyrrohdine Cuscohygrine Hygrine... 

Figure 11. L-ornithine is an important precursor of pyrrolidine, tropane and pyrrolizidine alkaloids.

Figure 15. L-ornithine and L-nicotinic acids are precursors of some aikaioids in the Nightshade famiiy.

The Borage plant (syn. Forget-me-not) family (Boraginaceae Lindl.) contains L-ornithine (Figure 11 and 15) derived alkaloids, such as indicine-N-oxide in the heliotrope (Heliotropium indicum) and southern hound s tongue Cynoglosum creticum) species (Table 8). Farsam et al. reported on new alkaloids from... 

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