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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,
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:
Additional recommended knowledge
Molecular Biology of the Cell, Alberts Et Al., James D. Watson
|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.|