Formation of ammonia and Urea cycle by Dr. Ashok Kumar J

For students and teachers

1. Protein metabolism and Urea Cycle Dr. Ashok Kumar J Associate Professor International School of Medicine Management and Science University Malaysia Dr Ashok Kumar J ; IMS; MSU 1

2. OBJECTIVES: To learn ……. Transamination reaction Deamination reaction Sources for ammonia Transport of ammonia Detoxification of ammonia (Urea cycle) Ammonia toxicity Hyperammonemia Dr Ashok Kumar J ; IMS; MSU 2

3. Catabolism of proteins C R H NH 2 COO - α -amino group α - carboxyl group Side chain group Individual amino acids differ from each other with respect to their side chain group Amino Acids Dr Ashok Kumar J ; IMS; MSU 3

4. Removal of the α amino group is an obligatory step in the catabolism of amino acids The α amino group is removed as Ammonia Ammonia is converted to Urea (in Liver) The carbon skeleton of the amino acid is metabolized - Energy production - Glucose synthesis - Fat synthesis Dr Ashok Kumar J ; IMS; MSU Cataboliosm of Amino acids C R H NH 2 COO - NH 3 UREA in Liver 4

5. Glucogenic amino acids Glucogenic and ketogenic Ketogenic amino acids Alanine, Arginine, Asparagine, Aspartate Asparagine, Cysteine, Methionine Glutamate, Glutamine, Glycine, Histidine Proline, Serine, Threonine,Valine Tyrosine Isoleucine Phenylalanine Tryptophan Leucine Lysine 5 Dr Ashok Kumar J ; IMS; MSU

6. Removal of Amino group of amino acid as ammonia Transamination Oxidative deamination Amino acid α - Ketoacid (carbon skeleton) Amonia Dr Ashok Kumar J ; IMS; MSU 6

7. Transamination Alanine αKetoglutarate Pyruvate Glutamate Transaminase (amino transferase) Pyridoxal phosphate (PLP) Transfer of amino group of an amino acid to ketoacid to form new Ketoacid corresponding to the original amino acid , and new amino acid corresponding to the original ketoacid α Ketoglutarate is a α ketoacid most frequently used in transamination reactions Transamination reaction does not form free ammonia 7 Dr Ashok Kumar J ; IMS; MSU

8. Transaminases are named after the specific amino group donor Alanine αKetoglutarate Pyruvate Glutamate Alanine amino transferase (ALT) Aspartate Oxaloacetate 8 Dr Ashok Kumar J ; IMS; MSU TCA Cycle TCA Cycle

9. Functions of Transamination reaction Amino acids are converted to their respective ketoacids (carbon skeleton) Further metabolized by TCA cycle to produce energy or used to form glucose or Fat 2. Helps in the synthesis of nonessential amino acids 9 Dr Ashok Kumar J ; IMS; MSU Amino acids which don't under go transamination – Lysine and threonine

10. Deamination Amino group of amino acid is removed as free ammonia Oxidative deamination Amino acids are oxidized (removal of Hydrogen) and the α amino group of the amino acid is removed as free ammonia 10 Dr Ashok Kumar J ; IMS; MSU

11. Oxidative deamination by L-Glutamate dehydrogenase Glutamate αKetoglutarate NH3 NAD + / NADP + NADH + H + / NADPH + H + L-Glutamate dehydrogenase + 11 Dr Ashok Kumar J ; IMS; MSU Allostearic regulators of L-Glutamate dehydrogenase Allostearic inhibitors: ATP, GTP Allostearic activator: ADP

12. L-amino acid oxidase L- Aminoacid αKetoacid NH3 FMN FMNH 2 O 2 H 2 O 2 2 H 2 O + O 2 Catalase 12 Dr Ashok Kumar J ; IMS; MSU L- aminoacid oxidase Requires FMN as the coenzyme Enzyme activity is low in kidney and liver It is of little importance D-amino acid oxidase Use FAD as coenzyme

13. Nonoxidative deamination Removal of the α amino group of amino acid as free ammonia without oxidation of the amino acid Dehydratase Acts on hydroxyl amino acids to remove ammonia Serine Pyruvate NH3 H 2 O Serine dehydratase PLP + 13 Dr Ashok Kumar J ; IMS; MSU

14. Transdeamination Alanine αKetoglutarate Pyruvate Glutamate Transaminase αKetoglutarate NH3 L- Glutamate dehydrogenase NADH+H + NAD + Transamination Oxidative deamination 14 Dr Ashok Kumar J ; IMS; MSU

15. NH 3 Sources of ammonia Catabolism of Purines and Pyramidines Catabolism of various nitrogen containing compounds Ammonia absorbed from the Gut Glutaminase action on glutamine 15 Dr Ashok Kumar J ; IMS; MSU

16. Blood level is about 80 to 100 μ g/dl Excess of Ammonia is toxic to the CNS Ammonia UREA Used for synthesis of glutamate and glutamine Excreted in urine Acts as buffer in kidney 16 Dr Ashok Kumar J ; IMS; MSU

17. Glutamate Glutamine Glutamine synthetase NH 4 + H 2 O ATP ADP Transport of ammonia 17 Dr Ashok Kumar J ; IMS; MSU Ammonia is transported as glutamine from CNS to liver Formation of glutamine is first line of defence against ammonia toxicity Glutamine is carried through blood to liver

18. Glutamine Glutamate Glutaminease NH 4 + H 2 O Glutamine converted to ammonia and glutamate in the liver by glutaminase 18 Dr Ashok Kumar J ; IMS; MSU From muscle ammonia is transported as Alanine

19. Urea Cycle 19 Dr Ashok Kumar J ; IMS; MSU

20. CO 2 NH 4 2ATP 2ADP Carbamoyl Phosphate Carbamoyl Phosphate Synthetase I + Ornithine Ornithine Transcarbamoylase L- Citrulline Argininosuccinate ATP L-Aspartate AMP+PPi Argininosuccinate Synthase L-Arginine Arginase Urea H 2 O Fumarate Argininosuccinate Lyase 20 Dr Ashok Kumar J ; IMS; MSU Aspartate TCA Cycle Mitochondria L- Citrulline

21. Regulation of urea cycle Carbamoyl phosphate synthetase I N- Acetyl glutamate + Synthesis of N-acetyl glutamate is enhanced by high protein diet and amino acids especially arginine 21 Dr Ashok Kumar J ; IMS; MSU

22. Heperammonemia Genetic defects of the urea cycle Blood level of ammonia is increased Ammonia has direct neurotoxic effect on the CNS Ammonia intoxication Symptoms : Tremors , Vomitting , slurring of speech, Blurring of vision coma accompanied by cerebral edema and increased cranial pressure If not treated – death 22 Dr Ashok Kumar J ; IMS; MSU Liver disease is the common cause Cirrosis of liver caused by alcoholism, hepatitis or biliary obstruction - results in flow of portal blood directly into systemic circulation In fulminant liver failure gut is sterilized to reduce further increase in blood ammonia

23. Glutamate is used for glutamine formation Depletion of Glutamate Glutamate is required for the synthesis of Gamma amino butyric acid (GABA) Depletion of inhibitory neurotransmitter GABA 23 Dr Ashok Kumar J ; IMS; MSU Ammonia reacts with α-ketoglutarate to form glutamate. Depleted levels of α-ketoglutarate I Impair function of the tricarboxylic acid (TCA) cycle in neurons Depletion of energy in neurons. Why ammonia is toxic to human body ?

24. Hereditary Hyperammoniemia Cause: Genetic deficiency of each of the five enzymes of urea cycle Hyperammonemia Type 1 Carbamoyl phosphate synthase I deficiency Hyperammonemia Type 2 deficiency of ornithine transcarbamoylase (OTC) Citrullinemia Defect in argininosuccinate synthase activity Argininosuccinicaciduria Absence of argininosuccinase Hyperargininemia Arginase activity is deficient 24 Dr Ashok Kumar J ; IMS; MSU

25. Thank you Dr Ashok Kumar J ; IMS; MSU 25