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A biochemical process involving the metabolism or formation of proteins. Proteins constitute one of the main ingredients of food. Proteins are substances with quite large molecules, which cannot be absorbed from the digestive system. It is, therefore, essential to be catabolized, that is splitted to their ingredients, called amino acids, which can be absorbed and enter the blood circulation. With this procedure, the organism can employ aminoacids and compose new proteins, essential for its construction and functioning. This procedure is known as protein synthesis. Splitting proteins (and other large molecules, too) by an organism is called catabolism. This procedure is more complicated for proteins, as these contain the element Nitrogen (N) in a group called amino group. The first step in protein catabolism is exactly this removal of amino group, called deamination. This is achieved by transferring the amino groups contained in all amino acids to only one, the glutamic acid. The chemical reactions involved are catalyzed by enzymes called transaminases. The next step is the dehydrogenation of the formed glutamic acid by means of a compound called NAD (Nicotinamide adenine dinucleotide) in the presence of water. The reaction is catalyzed by the enzyme glutamate dehydrogenase, producing ammonium ions (NH4+), Hydrogen cations (H+) and a compound called α-ketoglutarate. Ammonium anions are very toxic and cannot be absorbed by the organism. If they remain in the blood stream, they bypass the blood brain barrier, can cause encephalopathy and, finally, death. So ammonium ions are converted to urea, a soluble substance which can be excreted in urine. The rest of amino acids can follow different steps:
- Enter the citric acid cycle
- Converted to acetylCoA
- Enter the puryvate cycle
to produce energy.


Molecular Biology of the Cell, Alberts Et Al., James D. Watson

See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Proteinolysis". A list of authors is available in Wikipedia.
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