Glutamic acid labeled with ammonium

More specific labelling may be obtained in a biosynthetic process using enzymic methods of synthesis. The preparation of amino acids by the reductive amination of 2-keto acids is well known. Indeed, the synthesis of N-labelled amino acids by this route is among the earliest literature on the preparation of compounds labelled with stable isotopes [73], Such reductions can be carried out enzymically and L - [a- N] glutamic acid has been prepared in good yield from 2-oxoglutaric acid and N-labelled ammonium chloride in the presence of reduced nicotinamide adenine dinucleotide phosphate [74],... 

The ammonia enters the portal vein and mixes with the metabolic nitrogen pool of the body. The fixation of this ammonia nitrogen into arginine, glutamic acid and utamine and aspartic acid represents a net contribution to nitrogen balance. The alternative fate of this ammonia is its conversion to urea prior to renal excretion. Thus the use of N-labelled ammonium salts or [ N]urea forms the basis of several common lines of clinical investigation. 

The synthesis of N-labeled glutamic acid (glutamate [Glu, E]) has been reported to be effectively accomplished by mixing 2-ketoglutaric acid (a-ketoglutaric acid) in aqueous solution with N-enriched ammonium chloride and dilute sodium hydroxide. Then, as shown in Scheme 12.31, when that mixture is added dropwise over a period of about 5h to a suspension of reduced platinum oxide in water,... 

The total amount of urea synthesized each day is several-fold higher than the amount that is excreted. Urea diffuses readily from the bloodstream into the large intestine, where it is hydrolysed by bacterial urease to carbon dioxide and ammonium. Much of the ammonium is reabsorbed and used in the liver for the synthesis of glutamate and glutamine, and then a variety of other nitrogenous compounds. Studies with urea show that a significant amount of label is found in essential amino acids. This may reflect intestinal bacterial synthesis of amino acids, or it may reflect the reversibility of the transamination of essential amino acids. 

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