Ornithine formation

The glutamic semialdehyde formed in the intestine can also cyclize and be reduced to form proline. Therefore, proline is not an essential amino acid in people. Any amino acid that can form glutamate can be converted to glucose. Among the amino acids that can produce glutamate, which will be examined in more detail when they are discussed individually, are glutamine, arginine via ornithine formation, proline, and histidine. 

The m-Boc and S,m-bis-adamantyloxycarbonyl (Adoc) urethane derivatives of Arg have been used for Fmoc SPPS but appear to be inadequate for protection of the guanidino functionality and show substantial ornithine formation [176]. A ft>,a) -bis-Boc derivative has been reported to eliminate ornithine production, although lactam formation is not completely prevented [177]. 

In plants, the conversion of glutamic acid to ornithine occurs via acetyl-ated derivatives as in prokaryotes (Davis, 1955), but in animals acetylated derivatives are not involved (Meister, 1965). An earlier debate (Vogel and Bonner, 1954 Davis, 1955 Meister, 1965) over the role of acetylated intermediates in Neurospora crassa has been resolved by a surfeit of evidence that acetylglutamic acid participates in ornithine formation (Cybis and Davis, 1974, 1975 Weiss and Davis, 1973). In higher plants the evidence is less conclusive, but is strong enough to make the participation of acetylated compounds probable. 

Ornithine formation. Occurs when protonation or acyl-based groups are used for protection of the guanidine side-chain... 

Cystinuris Defective membrane ttansport in kidney and amall intestine. Excessive urinary excretion of cystine, lysine, arginine, and ornithine formation of cystine kidney stones. Restriction of dietary nteihionina high fluid intake alkelinizing urine possible penicillamine to increase solubility of cystina. 

Vogel discovered an alternate pathway of ornithine biosynthesis from glutamic acid involving AT-acetylglutamate 114, 116). He has obtained evidence that this is the major pathway for ornithine formation in E. colt and Neurospora 127). The pathway shown in Fig. 5 is of minor importance for ornithine biosynthesis but is the major one for proline. These conclusions have been substantiated by isotope competition experiments 128). The steps in the acetylglutamate pathway is shown in Fig. 6. 

Figure 29-9. Reactions and intermediates of urea biosynthesis. The nitrogen-containing groups that contribute to the formation of urea are shaded. Reactions and occur in the matrix of iiver mitochondria and reactions , , and in iiver cytosoi. COj (as bicarbonate), ammonium ion, ornithine, and cit-ruiiine enter the mitochondriai matrix via specific carriers (see heavy dots) present in the inner membrane of iiver mitochondria.

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... 

There are numerous abnormalities of cysteine metabolism. Cystine, lysine, arginine, and ornithine are excreted in cystine-lysinuria (cystinuria), a defect in renal reabsorption. Apart from cystine calculi, cystinuria is benign. The mixed disulfide of L-cysteine and L-homocysteine (Figure 30-9) excreted by cystinuric patients is more soluble than cystine and reduces formation of cystine calculi. Several metabolic defects result in vitamin Bg-responsive or -unresponsive ho-mocystinurias. Defective carrier-mediated transport of cystine results in cystinosis (cystine storage disease) with deposition of cystine crystals in tissues and early mortality from acute renal failure. Despite... 

By analogy with the asymmetrical incorporation of [2-14C] ornithine it was proposed (5,116,117) (Scheme 22) that to avoid the formation of putrescine... 

The pivotal role of hygrine in the biosynthesis of cuscohygrine and of the tropane alkaloids has justified numerous investigations. The following scheme represents the now generally admitted pattern of formation of these bases. Ornithine (119) is first converted to putrescine or V-methylputrescine (120)... 

The paper by Krebs and Henseleit (1932), Experiments on the Formation of Urea in Animal Bodies (Klinische Wochenschrift 11,759), contained the phrases... in the synthesis of urea in the living cell, ornithine acts like a catalyst. We therefore draw the conclusion. .. that the primary reaction for the synthesis of urea from ammonia is... 

Cohen and Grisolia then concentrated on the first step in the reaction, obtaining citrulline from ornithine. The reaction appeared to depend on oxygen, a requirement traced to the need for high concentrations of ATP. Physiologically the formation of urea occurs at very low levels of ammonia, which is extremely toxic as it is also lipid soluble and enters cells very easily. Cells are not very effectively buffered against OH. ... 

An anomaly associated with citrulline that became evident when detailed kinetic studies were made in the 1950s (R.B. Fisher and J.R. Bronk) was the irreproducibility of its catalytic activity in liver slices on the formation of urea, despite the clear evidence from Ratner and Petrack of its importance in arginine synthesis. Initially the discrepancy in catalytic activity between ornithine and citrulline was ascribed to the possible impermeability of the liver cell plasma membrane to the latter intermediate, a hypothesis which was rapidly disproved experimentally. Only recently has it been shown that ornithine transcarbamylase is clearly associated with the ornithine/... 

The free a-amino groups of the ornithine units were also found in an acetylated form 90, 243). Since triacetylfusigen is resistant to hydrolysis, formation of the acetylated mono-, di-, and trimeric linear acetylfusarinines is assumed to be effected by enzymatic cleavage 103a, 243). X-ray and CD data of the Fe " complex of triacetylfusigen have been obtained 152). Depending on the solvent used for crystallization the crystals show A-cis or A-cis configuration, while in solution A-cis prevails. 

This enzyme [EC 3.5.3.1], also referred to as arginine amidinase and canavanase, catalyzes the hydrolysis of arginine resulting in the formation of urea and ornithine. The enzyme, which uses a manganese ion as a cofactor, will also utilize a-/V-substituted E-arginines and canavan-ine as substrates. 

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. 

Examples of amines that frequently occur in fish muscle include cadaverine from lysine, putrescine from ornithine and histamine from histidine. Histamine, because of its involvement in Scombroid food poisoning (histamine intoxication), has been extensively studied with respect to factors influencing its formation in many different fish species. Tuna and other fish from the families Scomberesocidae and Scombridae and a non-scombroid fish, mahi-mahi (dolphin fish) have been most... 

Robins, R. J., Parr, A. J. and Walton, N. J. 1991. Studies on the biosynthesis of tropane alkaloids in Datura stramonium L. transformed root cultures. 2. on the relative contributions of L-arginine and L-ornithine to the formation of the tropane ring. Planta, 183 196-201. 

M. J. C. 1990. Over-expressing a yeast ornithine decarboxylase gene in transgenic roots of Nicotiana rustica can lead to enhanced nicotine formation. Plant Molecular Biology, 15 111-114. 

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