Biochemistry of Amino Acids - A. Meister 1961

General Biochemistry and Physiology of Amino Acid Metabolism
Synthesis of Peptide Bonds
Acylation of Amino Acids

It has long been known that hippuric acid (benzoylglycine) is a normal constituent of urine in A number of animals (such as the horse, dog, and rabbit) as well as humans, and that benzoic acid introduced into the Organism is excreted primarily as hippuric acid. The excretion of hippuric acid following the administration of a specific dose of sodium benzoate is used as an indicator of Liver function in humans. In birds (such as chickens), the "detoxification" of benzoic acid leads to the excretion of ornithuric acid; phenylacetic acid in chickens also combines with Ornithine. In humans, the administration of phenylacetic acid results in the excretion of phenylacetylglutamine.

The Biosynthesis of acylamino acids has attracted interest not only because of its role in METABOLISM, but also because its investigation can provide valuable insights into peptide bond synthesis. The synthesis of hippuric acid was first demonstrated in experiments using liver and Kidney slices [509]. An analogous reaction—the synthesis of p-aminohippuric acid—is carried out in the same tissue slices [510]. These reactions were subsequently studied in homogenate enzyme systems as well [510–513]. The liver Enzymes involved are apparently localized in the mitochondrial fraction [511, 514]. Neither benzoyl phosphate nor N-phosphoglycine is utilized in this reaction. At the same time, it was found that coenzyme A is required for this reaction [515], and it has recently [516] been proven that the following reactions take place:

1) АТФ + Кофермент А + Бензойная кислота →

→ Бензоил-кофермент А + АМФ + Пирофосфат,

2) Бензоил-кофермент А + Глицин → Бензоилглицин + Кофермент А.

The synthesis of p-aminoornithuric acids from a- and S-N-benzoylornithine and p-aminobenzoic acid was studied by McGilvrey and Cohen [517], who used a cytoplasmic granule preparation from chicken Kidneys. The enzyme system synthesizing p-aminoornithuric acid is in many respects similar to the rat liver system that synthesizes p-aminohippuric acid. The possible role of coenzyme A in The formation of ornithuric acids has not yet been investigated. The overall reactions described above can be represented as follows:

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A number of other acylation reactions occur in living organisms; these include the acylation of Cysteine and its derivatives [518–522] and the formation of phenylacetylglutamine [523–526]. The Acetylation of glutamic acid has been observed in Escherichia coli (p. 345); the reaction apparently requires the presence of coenzyme A. The presence of acetylaspartic acid in cat Brain tissue indicates that an analogous reaction takes place in this tissue (p. 14). The acetylation of Amino Acids in the presence of cyanide was observed in experiments with dried Cell preparations of Clostridium kluyveri [527]. Further studies indicate that in this system, the direct donor of the acetyl group is acetyl phosphate, and that the reaction proceeds with the participation of phosphotransacetylase and coenzyme A [528].