Content: 1. Introduction to the metabolism of proteins and amino acids. 2. Amino acid degradation. 3. Degradation of amino acid carbon skeletons. 4. Formation. Jump to Amino acid metabolism - The following list contains links to information about the metabolism of individual amino acids. Positively charged side. Introduction. All tissues have some capability for synthesis of the non-essential amino acids, amino acid remodeling, and conversion of non-amino acid carbon skeletons into amino acids and other derivatives that contain nitrogen. However, the liver is the major site of nitrogen metabolism in the body.


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This transporter keeps the brain supplied with all aromatic amino acids. Since tryptophan is the precursor of the neurotransmitter serotonin, the competitive inhibition of its transport to the brain results in a lack of cerebral serotonin [ 74 ], amino acid metabolism is believed to cause the observed deficits in brain function and development.

In addition to phenylalanine itself, some aberrant metabolites derived from it also occur at increased levels, and the appearance of ketone derivatives such as phenylpyruvic acid in the urine has given the disease its name.

These metabolites have no proven connection to the pathogenesis of the amino acid metabolism.


Limitation of dietary phenylalanine. The challenge, then, amino acid metabolism to diagnose the disease in newborn kids, before any damage is done.

Happily, the enzyme defect does not cause a problem during fetal development, since the placenta constantly equilibrates both useful and potentially harmful metabolites between the maternal and the fetal circulation.

Metabolism of Amino Acids

The modern test for phenylketonuria is effective but boring—a sample of blood is drawn, and the phenylalanine concentration in the serum is determined by HPLC. The original test—the Guthrie test—was a bit more roundabout in principle, yet ingenious and exceedingly simple and amino acid metabolism in practice.

Moreover, it well illustrates the power of bacterial genetics in biochemistry, and it therefore merits discussion here.


In contrast to mammalian cells, the bacterium Escherichia coli amino acid metabolism synthesize all 20 standard amino acids, as long as it has ammonia, some inorganic salts, and an organic carbon source such as glucose.

Such a substrate mixture constitutes a minimal medium. The Guthrie test makes use of a mutant E.

This strain can be grown on a rich medium that supplies phenylalanine; however, when spread onto minimal medium, it will not grow. Now, if we take a little snippet of filter paper soaked with a drop of baby blood and place it on top of the inoculated minimal medium, any phenylalanine contained in it will amino acid metabolism into the surrounding agar.

If there is enough of it amino acid metabolism the sample, this will allow the bacteria in the vicinity to resume growth.

Amino acid metabolism

Therefore, a zone of bacterial growth surrounding a blood sample will identify a patient with phenylketonuria. Note that, for amino acid metabolism test to work, we cannot collect the blood sample right away after birth.

This is a drawback of the test relative to the HPLC method—the latter is more quantitatively accurate and readily detects the smaller increase in phenylalanine concentration that amino acid metabolism present at the time of delivery.

Ochratoxin A competitively inhibits the coupling of phenylalanine to its cognate tRNA by the corresponding aminoacyl transferase and thereby disrupts protein synthesis. It is more toxic to fetuses than to adults, most likely because fetuses are short of the enzymes that inactivate xenobiotics and toxins such as ochratoxin.

Mothers who are heterozygous for PKU will have a somewhat higher level of phenylalanine, which will be shared with the fetus via the placenta. This will counter the inhibition of tRNA aminoacylation in the fetus and amino acid metabolism afford it some measure of protection.


One of the places with the highest abundance of PKU is Ireland. This country amino acid metabolism also known for its repeated historic episodes of severe famine.

Protein metabolism

Starving people will tend to eat rotten food rather than discard amino acid metabolism. Indeed, reference [ 75 ] reports that, among Irish women, lower rates of abortion were found in those who were heterozygous for PKU.

I have not ascertained whether the time periods covered by those statistics coincided with periods of actual famine. In this case, there seems to be no heterozygote advantage; instead, the high incidence is due to the so-called founder effect, that is, the common descent of the afflicted population from a small group of founding settlers that happened to contain one or several carriers of the gene.

Refer to slide The resulting 2-oxo acids amino acid metabolism and pyruvate are involved in energy metabolism within cells.

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