Almaaqal University Biochemistry Metabolism of Protein and Amino Acids Lecture Notes PDF

Almaaqal University Metabolism of Protein and Amino Acids Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-11  Introduction to amino acid and protein metabolism The amino...

Almaaqal University Metabolism of Protein and Amino Acids Dr/ Wael Sobhy Darwish Biochemistry PhD Lec-11  Introduction to amino acid and protein metabolism The amino acid metabolism is the biochemical pathways that produce, break down, and use amino acids. The body uses amino acids to make proteins, enzymes, hormones, and also precursors to many important substances for the body as biogenic amines, Hemoglobin formation or purines and pyrimidines (genetic material synthesis).  GENERAL CATABOLIC PATHWAYS OF AMINO ACIDS Unlike fats and carbohydrates, there is no dedicated storage of proteins and amino acids in the human body. In human, the end products of protein and amino acids catabolism are ammonia and urea. They are produced through the following catabolic pathways. Transamination. Deamination: Oxidative - Non oxidative - Hydrolytic. Transdeamination:. Decarboxylation.  1.Transamination Amino acid metabolism starts with a protein being broken down into amino acids, which are the building blocks for protein synthesis. Then, these amino acids can undergo an important reaction involved in amino acid metabolism called transamination. The nitrogen of the amino groups (amino nitrogen) can not be used for energy production and must be removed from our body. The first way is an amino nitrogen conversion to a urea (about 95 %), followed by urea excretion from the body via the urine. The major organ responsible for transamination reactions is the liver.  Transamination Definition: It is the transfer of amino group from α-amino acid to α-ketoacid to form a new α-amino acid and a new α-ketoacid  Mechanism 1. By enzymes called transaminases (or amino transferases) catalyze transamination. 2. Pyridoxal phosphate (PLP = active vitamin B6) is the coenzyme of all transaminases. 3. For all amino acids except: (lysine, threonine, proline and hydroxyproline). 4. All transamination reactions are reversible. 5. Present either in cytosol or in both cytosol and mitochondria of most tissues. 6. Among all transaminases, 3 are present in most mammalian tissues and they are of clinical importance. These are: ALT, AST and glutamate transaminase The difference between AST and ALT, is that ALT is found mainly in liver, with negligible quantities in the kidneys, heart, and skeletal muscle, while AST is found in the liver, heart, skeletal muscle, kidneys, brain, and red blood cells. As a result, ALT is a more specific indicator of liver inflammation than AST.  Oxidative deamination Is the removal of an amino group from a molecule. Enzymes that catalyze this reaction are called deaminases. During oxidative deamination amino group is converted to keto group with simultaneous release of NH4 SITE (Mostly in liver and kidney).  The resulting NH4+ enters the urea cycle and α-ketoglutarate may be used in the transamination or Krebs cycle. We can conclude that most of the amino acid undergoes transamination in its degradation and that the majority of amino nitrogen from amino acids is directly or indirectly concentrated in the molecule of glutamate / glutamine.  TRANSDEAMINATION Definition: - It is transamination of most amino acids with α-Ketoglutarate to form glutamate, Then glutamate is deaminated to give ammonia (NH3). - It is the main pathway by which amino group (NH2) of most amino acids is released in the form of ammonia (NH3).  DECARBOXYLATION Definition: removal of CO2 of amino acids produces the corresponding amines. Functions: Some amines have important biologic functions: e.g. 1. Histamine (from histidine) is vasodilator. 2. γ-Amino butyric acid (from glutamate) is neurotransmitter. Destruction of amines - The resulting amines are further oxidized -after carrying out their functions by amine oxidase enzymes.