Ammonia Production from Arginine

Microscopically, it may be difficult to separate heterofermentative cocco bacilloid Leuc oenos) from short bacilloid bacteria Lactobacillus sp). In these cases, Garvie, (1960, 1967) suggests that separation should be made using ammonia formation from arginine. Upon complete conversion of L-arginine, 2NH3 would be expected  

Reaction 1 arginine deiminase Reaction 2 ornithine transcarbamylase Reaction 3 carbamyl kinase 

Most heterofermentative lactobacilli are positive (producing NHg), whereas Leuc oenos is negative (not producing detectable NHg). However, Pilone et al. (1991) suggest that some heterofermentive lactobacilli are capable of carrying out only the first two steps, and, hence, the second molecule of NH3 is not produced. In these cases, the concentration of ammonia produced is below detection limits (see Supplemental Notes 1 and 2). 

Arginine Broth Test tubes and stoppers Coors porcelin spot plate Nessler s Reagent  

In a 1-L flask, dissolve 50 g potassium iodide in 400-500 mL cold distilled or deionized water. 

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The major emphasis in this chapter related to excretion is on ammonia and urea, particularly on the control of the latter as the normal excretion product. There are two major nitrogenous precursors of urea ammonia and aspartate. Before delving into the mechanism and control of urea synthesis, it would be wise to look at the different ways that these precursors can arise and the important tissues concerned with urea synthesis. In people, the predominant synthesis of urea occurs in the liver, with very small amounts of urea formed from arginine in other tissues. The complete synthesis of urea, from amino acids and other nitrogen sources, occurs via a process known as the urea cycle. 

The aspartate entering the cycle is produced by reaction of glutamate with ox-alacetate, the former being produced from a-ketoglutarate plus ammonia released by deamination of an amino acid. The oxalacetate is derived from the fumarate released in the production of arginine from ai inosuccinate, which enters the tricarboxylic acid cycle and is converted to malate and then oxalacetate. We then have a second associated cycle linking the luea and the tricarboxylic acid cycles, which may be visualised as shown in Fig. 9.13. 

Most of the ammonia (NH,) produced through deamination—removal of amino groups (NH,) from amino acids is converted to urea in the liver for excretion by the kidneys. To facilitate elimination, 1 mole of ammonia (NH,) combines with 1 mole of carten dioxide (CO,), another metatelic waste product. This compound is then phosphorylated to produce carbamyl phosphate. Carbamyl phosphate then combines with ornithine to form citrulline an intermediate in the urea cycle. The amino acid, aspartic acid, contributes another amino group (NH,), and citrulline is then converted to the amino acid arginine. Urea splits off from arginine forming ornithine, and the cycle is completed. Fig. U illustrates the urea cycle. 

A diet low in protein reduces ammonia production and is the only treatment at present available. It reduces seizure frequency it may prevent mental retardation if given from earliest infancy. In the case of argininosuccinic aciduria, additional arginine must be added to the low protein diet, otherwise the children deteriorate, arginine being an essential amino acid in this condition. 

The concept of the ornithine cycle arose from the observation that ornithine, citrulline and arginine stimulated urea production in the presence of ammonia without themselves being consumed in the process. 

Alanine and aspartic acid are produced commercially utilizing enzymes. In the case of alanine, the process of decarboxylation of aspartic acid by the aspartate decarboxylase from Pseudomonas dacunhae is commercialized. The annual world production of alanine is about 200 tons. Aspartic acid is produced commercially by condensing fumarate and ammonia using aspartase from Escherichia coli. This process has been made more convenient with an enzyme immobilization technique. Aspartic acid is used primarily as a raw material with phenylalanine to produce aspartame, a noncaloric sweetener. Production and sales of aspartame have increased rapidly since its introduction in 1981. Tyrosine, valine, leucine, isoleucine, serine, threonine, arginine, glutamine, proline, histidine, cit-rulline, L-dopa, homoserine, ornithine, cysteine, tryptophan, and phenylalanine also can be produced by enzymatic methods. 

Location of Ureagenesis.— It has been suggested that ureagenesis is a property of most tissues, but perfusion and incubation experiments have shown that the mechanism is narrowly restricted to the liver, and there is no evidence that urea can be assembled from ammonia and carbon dioxide in any other tissue in the mammal, although the presence of arginase in the kidney may account for a slight subsidiary extra-hepatic production of urea from surplus arginine. 

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