Amino acid deamination

The anaerobic mode of protein utilization is entirely possible in theory and in practice. Oxygen is not required for protein and nitrogen catabolism until the final stages of amino acid deamination have been reached. Complete anaerobic catabolism of proteins and nitrogen compounds (to the point where the final products C02, HjO and NH3 appear) has been known for a long time in prokaryotic organisms, but in eukaryotes only in parasitic worms, which are obligate anaerobes (von Brand, 1946). However, in recent decades, anaerobic metabolism of proteins has been found in some aquatic... 

Boon, P. I., Moriarty, D. J. W., and Saffigna, P. G. (1986). Rates of ammonium turnover and the role of amino acid deamination in seagrass Zostera capricornii beds of Moreton Bay, Australia. Mar. Biol. 91, 259-268. 

How are the other amino acids deaminated Most are transaminated, transferring their N to make glutamate ... 

Contrary to the case of free a-amino acids, deamination-substitution of esters of a-amino acids generally proceeds with racemization with excess inversion about the a-carbon atom. However, reaction of the ethyl ester of phenylalanine and its derivatives with sodium nitrite in trifluoroacetic acid affords substitution products with retention of configuration and migration products with inversion of configuration. This result may be explained by assuming initial formation of the phenonium intermediate (2 Scheme 6). ... 

Microorganisms and some plant tissues are capable of catalyzing a multiplicity of nonoxidative amino acid deamination reactions. It is beyond the scope of this chapter to review these systems, since for the most part they have not been studied with cell-free preparations. Two exceptions to the latter statement are the aspartase and tryptophanase systems. The latter is discussed in the chapter, Carbon Catabolism of Amino Acids. 

Other types of nonoxidative amino acid deamination are as follows ... 

One instance is known of more or less specific patholojpcal disturbance of transamination, namely, the marked decrease in -aph and as-aph activity in all tissues of severely thiamine-deficient pigeons and rats, described by Kritzmann (118, 119) the rates of l>amino acid deamination and of re-ductive amination of PU are similarly lowered, while the activity of d-amino acid oxidase and of glutamic dehydrogenase is not impiured. Absence of these effects in starved controls and the rapid restoration of aph activity upon administration of thiamine rule out a non-specific effect of lowered protein intake. 

Although the equilibrium of this reaction is very much in favour of glutamate formation, in the cell the rapid removal of the 2-oxoglutarate and NAD(P)H allows the enzyme to function efficiently in the direction of glutamate deamination. Liver glutamate dehydrogenase is a very active enzyme, and the reaction is not rate-limiting for amino acid deamination. 

The ammonia resulting from amino acid deamination is eliminated in one of three ways depending on the organism. Fish and other aquatic animals simply excrete the ammonia to their aqueous surroundings, but terrestrial organisms must first convert the ammonia into a nontoxic substance—either nrea for mammals or uric acid for birds and reptiles. 

Early experiments by Borchers (1965) indicated that the supplementation with 1 g of thymol per 1 L of ruminal fluid in the presence of casein causes accumulation of amino acids and a decrease in the concentration of ammonia nitrogen, which snggests that amino acid deamination is hindered by ruminal bacteria. Broderick and Balthrop (1979) in their research conflrmed the inhibition of amino acid deamination resulting from the thymol supplementation. 

Borchers R (1965) Proteolytic activity of rumen fluid in vitro. J Anim Sci 24 1033-1038 Briskin DP (2000) Medicinal plants and phytomedicines. Linking plant biochemistry and physiology to human health. Plant Physiol 124 507-514 Broderick GA, Balthrop JE (1979) Chemical inhibition of amino acid deamination by ruminal microbes in vitro. 1 Anim Sci 49 1101-1111... 

The daily requirement of vitamin Bj appears to be proportional to the food intake, and Drummond suggests that this is because the vitamin is concerned both in amino acid deamination and in urea formation, which would explain the fact that both liver and kidney are very rich in riboflavin. The human requirement for normal health is estimated to be 40 to 50 y of riboflavin per 100 kilocalories of food (Sherman and Lanford, 1938 Bessey, 1938). 

Broderick, G.A. and J.E. Balthrop, Jr, 1979. Chemical inhibition of amino acid deamination by ruminal microbes in vitro. J. Anim. Sci. 49,1101-1111. 

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