Catabolism of amino acids, transamination and deamination

Sure! Here is a detailed note on the catabolism of amino acids:

Catabolism of amino acids is the process by which proteins are broken down into their constituent amino acids, which can then be further broken down and utilized by the body for energy production or to synthesize new proteins. This process is crucial for providing the body with the necessary building blocks and energy it needs to function properly.

1. Transamination: The first step in amino acid catabolism is often transamination, where an amino group is transferred from an amino acid to a keto acid, forming a new amino acid and a new keto acid. This process is catalyzed by enzymes called transaminases or aminotransferases.

2. Deamination: After transamination, the amino acids undergo deamination, where the amino group is removed from the amino acid. There are two main pathways for deamination:
- Oxidative deamination: In this process, the amino group is removed from the amino acid in the form of ammonia (NH3), which is then converted to urea in the liver through the urea cycle and excreted in urine.
- Non-oxidative deamination: This process involves the direct removal of the amino group from the amino acid without the formation of ammonia. This can occur through various enzymes and pathways depending on the specific amino acid.

3. Carbon Skeleton: After deamination, the remaining carbon skeleton of the amino acid can be used for energy production through several different pathways. These pathways include:
- Glycolysis: Some amino acid carbon skeletons can be converted into intermediates of glycolysis, such as pyruvate or acetyl-CoA, to generate ATP through cellular respiration.
- Citric acid cycle (Krebs cycle): Other amino acid carbon skeletons can enter the citric acid cycle to produce energy in the form of ATP.
- Gluconeogenesis: Some amino acids can also be converted into glucose through gluconeogenesis, providing a source of energy for tissues that require glucose but cannot produce it themselves.

4. Urea Cycle: The ammonia produced during deamination is toxic to the body and must be eliminated. The liver converts the ammonia into urea through the urea cycle, which is then excreted in urine. The urea cycle helps maintain nitrogen balance in the body by ensuring that excess nitrogen is safely eliminated.

Overall, the catabolism of amino acids is a complex process involving multiple biochemical pathways that play a crucial role in providing the body with energy and essential building blocks for growth, repair, and metabolism. It is tightly regulated to ensure proper functioning and to prevent the accumulation of toxic byproducts like ammonia.

1. CATABOLISM OF AMINO ACIDS DR.ANEEKA EHSAN (PT) CONTENTS Introduction to amino acids Catabolism of amino acids Transamination Deamination

2. AMINO ACID O rganic compounds that contain an amino group (NH2), a carboxyl group (COOH), and a side chain (R group) that is unique to each amino acid. Building blocks of proteins. 20 different amino acids. C ommonly found in proteins. CLASSIFICATION E ssential amino acids N on-essential amino acids

3. ESSENTIAL & NON-ESSENTIAL AMINO ACIDS Essential amino acids cannot be produced by the body and must be obtained from the diet. These include: Non-essential amino acids can be produced by the body, but they are still important for overall health. These include: Histidine,Isoleucine,Leucine , Lysine , Methionine , Phenylalanine , Threonine , Tryptophan , Valine Alanine,Arginine , Asparagine , Aspartic acid,Cysteine , Glutamine , Glutamic acid,Glycine , Proline,Serine

4. SOURCES OF AMINO ACIDS ESSENTIAL AMINOACIDS  Foods that contain all nine essential amino acids are called   complete proteins , (animal sources: beef, poultry, fish, eggs, dairy, soy). Foods that contain some but not all the essential amino acids are called incomplete proteins,  (plant sources: nuts, seeds, beans, legumes, chickpeas and some grains). NON-ESSENTIAL AMINOACIDS Synthesized from essential amino acids obtained from diet. M ainly synthesized from glucose , except for tyrosine i.e. synthesized from  phenylalanine .

5. AMINO ACID CATABOLISM T he breakdown of amino acids into simpler molecules. Amino acids, the building blocks of proteins, play a pivotal role in various biological processes, including protein synthesis, enzyme function, and hormone production. However, excess amino acids must be efficiently removed from the body by the process, known as amino acid catabolism , involves the breakdown of amino acids into simpler molecules for energy production or excretion. Primarily occurs in the liver.

6. AMINO ACID CATABOLISM STEPS INVOLVED: Transamination Deamination Urea cycle Carbon skeleton utilization: for energy production in the mitochondria or for the synthesis of new amino acids in the cytoplasm.

7. The carbon skeleton can be used for glucose formation by gluconeogenesis or for ATP production in the Krebs cycle, followed by the respiratory chain.

8. TRANSAMINATION Amine groups can be transferred or removed through transamination or deamination, respectively. Crucial Step in Amino Acid Catabolism. A reversible process, initiates the catabolism of amino acids. During transamination, the amino group (-NH2) of an amino acid is transferred to a keto acid, forming a new amino acid and releasing an α-keto acid. R eaction is catalyzed by enzymes called transaminases. Transamination is used to synthesize nonessential amino acids.

9. TRANSAMINATION MECHANISM Amino acid binding : The amino acid binds to the active site of the transaminase enzyme. Amino group transfer: The amino group is transferred from the amino acid to the pyridoxal phosphate (PLP) cofactor bound to the transaminase. Keto acid binding : A keto acid binds to the active site of the transaminase. Amino group transfer : The amino group is transferred to the keto acid, forming a new amino acid. α-keto acid release: The α-keto acid is released from the transaminase.

10. DEAMINATION A n irreversible chemical reaction that removes an amino group (-NH2) from an amino acid, resulting in the formation of a keto acid and ammonia (NH3). E nzymes: deaminases. Types (2): Oxidative deamination Non-oxidative deamination MECHANISM : The amino acid binds to the active site of the deaminase enzyme. The amino group is transferred to the deaminase enzyme. Ammonia (NH3) is released from the deaminase enzyme. The remaining part of the amino acid is converted to a keto acid.

11. EXAMPLE The general reaction for deamination of an amino acid can be represented as follows: Amino Acid → Keto Acid + Ammonia Here, the amino acid is transformed into a keto acid (also known as an alpha-keto acid or 2-oxo acid), and the amino group is released as ammonia. For example , consider the deamination of the amino acid alanine: Alanine → Pyruvate + Ammonia In this reaction, the amino group is removed from alanine, resulting in the formation of pyruvate and ammonia.

12. TYPES OF DEAMINATION Oxidative deamination : Involves the removal of an amino group (-NH2) from an amino acid through oxidation. The general reaction: Amino Acid + Oxygen → Keto Acid + Ammonia + Hydrogen Peroxide In this process, molecular oxygen is used to oxidize the amino acid, resulting in the removal of the amino group as ammonia. The remaining carbon skeleton is transformed into a keto acid. h ydrogen peroxide (H2O2) is produced as a byproduct. Example : Glutamate +Oxygen → Alpha-Ketoglutarate + Ammonia + Hydrogen Peroxide The ammonia produced is eventually converted into urea in the liver through the urea cycle, making it less toxic for excretion. Enzyme : glutamate dehydrogenase

13. TYPES OF DEAMINATION Non-oxidative deamination: P rocess in which an amino group (-NH2) is removed from an amino acid without the involvement of oxygen. The general reaction: Amino Acid → Keto Acid + Ammonium Ion Importantly, instead of forming ammonia as in oxidative deamination, a positively charged ammonium ion ( NH 4+​ ) is produced. Enzymes: dehydratases Example: Glutamine → Glutamate + Ammonium Ion The ammonium ion produced is eventually processed and excreted by the body. It can be incorporated into the urea cycle in the liver, where it is converted into urea and then excreted in the urine. Enzyme : glutaminase

14. HYPERAMMONEMIA The potential problem with deamination is that too much ammonia is toxic, causing a condition known as hyperammonemia . SYMPTOMS: Feeling irritable Lack of energy/ mental alertness Nausea & headache Behavioral changes Lack of muscle coordination ( difficulty in walking or speech) CAUSES: Genetic disorders Acquired health problems ( liver disease or kidney failure) Cirrhosis of liver (major cause in adults)

15. Our body has a method to safely package ammonia in a less toxic form to be excreted. This safer compound is urea . Most urea is then secreted from the liver and incorporated into urine in the kidney to be excreted from the body.