5-amino Acid Catabolism I(12 Oct)

Amino acid catabolism I

Dr. Mohammad Akram

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Catabolism?

is the set of metabolic pathways that break down molecules into smaller units and release energy.

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General Catabolic Process In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides and amino acids , respectively. As molecules such as polysaccharides, proteins and nucleic acids are made from long chains of these small monomer. 3

Catabolism Process (example) Protein Amino acid Acetyl-CoA (acetyl coenzyme A) Citric acid cycle

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20 Amino acids 1. alanine 2. arginine 3. asparagine

1. leucine 2. lysine

4. aspartic acid

3. Methionine

5. cysteine

4. phenylalanine

6. glutamine

5. proline

7. glutamic acid 8. glycine

6. serine

9. histidine

7. threonine

10. isoleucine

8. tryptophan 9. tyrosine 10. valine

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Amino Acid Requirements of Humans -------------------------------------------------------------------Nutritionally Essential Nutritionally Nonessential -------------------------------------------------------------------Argininea Alanine Histidine Asparagine Isoleucine Aspartate Leucine Cysteine Lysine Glutamate Methionine Glutamine Phenylalanine Glycine Threonine Proline Tryptophan Serine Valine Tyrosine --------------------------------------------------------------------a “ Nutritionally semiessential.” Synthesized at rates inadequate to support growth of children.

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Amino acid catabolism The carbon frames of amino acids are broken down into metabolites that can either be oxidized into CO2 and H2O to generate ATP (Adenosine-triphosphate) , or can be used for gluconeogenesis. The catabolism of amino acids accounts for 10 to 15% of the human body’s energy production.

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Amino acid catabolism cont. Each of the 20 amino acids has a separate catabolic pathway, yet all 20 pathways converge into 5 intermediates, all of which can enter the citric acid cycle. From the citric acid cycle the carbon can be completely oxidized into CO2.

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Citric acid cycle The citric acid cycle — also known as the tricarboxylic acid cycle (TCA cycle), the Krebs cycle, is a series of enzymecatalysed chemical reactions, which is of central importance in all living cells. The citric acid cycle occurs in the matrix of the mitochondrion.

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Nonessential Amino acids

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Alanine Catabolism Alanine is important in inter-tissue nitrogen transport as part of the glucose-alanine cycle. Alanine's catabolic pathway reaction produces pyruvate. Generally pyruvate produced by this pathway will result in the formation of oxaloacetate reacts with Acetyl CoA to form citrate. Although when the energy charge of a cell is low the pyruvate will be oxidized to CO2 and H2O. 12

Ornithine Ornithine, in excess of urea cycle needs, is transaminated to form glutamate (Transamination of α-ketoglutarate gives glutamate) semialdehyde. Glutamate semialdehyde can serve as the precursor for proline biosynthesis or it can be converted to glutamate. (Many semialdehyde's are intermediates in the biosynthesis and metabolic degradation of amino acids) 13

Proline Proline catabolism is a reversal of its synthesis process. The glutamate semialdehyde generated from ornithine and proline catabolism is oxidized to glutamate by an ATPindependent glutamate semialdehyde dehydrogenase. The glutamate can then be converted to α-ketoglutarate in a transamination reaction. 14

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Serine Catabolism The conversion of serine to glycine and then glycine oxidation to CO2 and NH3. Serine can be catabolized back to the glycolytic intermediate, 3phosphoglycerate, by a pathway that is essentially a reversal of serine biosynthesis.

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Glycine Catabolism Glycine is classified as a glucogenic amino acid, since it can be converted to serine by serine hydroxymethyl transferase and serine can be converted back to the glycolytic intermediate, 3 phosphoglycerate or to pyruvate by serine/threonine dehydratase. Nevertheless, the main glycine catabolic pathway leads to the production of CO2 and ammonia.

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Phenylalanine and Tyrosine catabolism

Will be discussed in a separate session

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Thank you for your attention

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