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Explain the fate of carbon skeleton and nitrogen group of amino acids. Explain the ways of transport of nitrogen from various parts of the body to the liver Describe the urea cycle and the enzymes involved in production of urea in the liver Define and classify Hyperammonemias. List the enzymes deficient in various hyperammonemias and its clinical features

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Amino group NH 3 Formation of urea Carbon skeletons Formation of Glucose and Ketone bodies.

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FATE OF THE CARBON SKELETONS Carbon skeletons are used for energy Glucogenic: TCA cycle intermediates or Pyruvate (Gluconeogenesis) Ketogenic: Acetyl CoA, Acetoacetyl CoA, or Acetoacetate

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PROTEINS Gastric juice ( acidity denatures proteins ) Intestinal enzymes hydrolyze AMINO ACIDS Amino acid transporters Na+Amino acid symporter (can take up di and tri peptides ) UPTAKE DEFECTS :- 1)Hartnups disease Long neutral amino acid transporter defect( Trp is not taken up Pellagra like symptoms as Trp Niacin is not formed ) 2)Cystinuria Basic amino acid transporter defect that also transports cysteine Urinary stones.Cystine forms Cystine by disulfide linkage (less soluble Stones )

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Difference btw total nitrogen intake and total nitrogen loss in feces POSITIVE NITROGEN BALANCE MORE NITROGEN INGESTION THAN LOSS Growing infants and pregnant women NORMAL BALANCE INTAKE MATCHES OUTPUT Normal Individuals NEGATIVE BALANCE NITROGEN OUTPUT EXCEEDS INTAKE Following surgery, cancer, malnutrition (decreased protein intake )

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OVERVIEW OF AMINO ACID METABOLISM ENVIRONMENT ORGANISM Ingested protein Bio- synthesis Protein AMINO ACIDS Nitrogen NH 3 Carbon skeletons Urea Degradation (required) 1 23 a b Purines Pyrimidines Porphyrins cc Used for energy pyruvate -ketoglutarate succinyl-CoA fumarate oxaloacetate acetoacetate acetyl CoA (glucogenic)(ketogenic) Recycling

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Affects central nervous system 1.Alkalization of intracellular compartment 2.Disrupts oxidative phosphorylation ATP depletion 3.Increased glutamate in Brain 4.Decreased Neurotransmitters GABA convulsions 5.Cerebral edema

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Symptoms of AMMONIA toxicity Flapping Tremor (Asterixis) ( Correlate flapping tremor later on with Liver failure in Clinical medicine ) Slurred Speech Blurred Vision COMA Death

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Ammonotelic Fishes Lots of water available Uricotelic Reptiles and birds Birds have to keep minimum body weight for flight Ureotelic Mammals

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Body Proteins Amino acids Catabolism UREA 25% 80-85%

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Sources of Amino Acids : Exogenous Diet Endogenous 1.Breakdown of muscle protein 2.Biosynthesis from intermediates of citric acid cycle. Utilization of Amino acids: Synthesis of New proteins Formation of Nucleotides Formations of Porphyrins and Catecholamines Production of energy and Ammonia.

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1) Reutilization: Glutamate and Glutamine are involved in recycling of amino acids. Glutamate + AmmoniaGlutamine Glutamine Synthase ATPADP They are secreted by the peripheral tissues in form of glutamine which is taken up by hepatocytes where the NH3 is re-used for amino acid and nucleotide synthesis Glutamine Glutamate + Ammonia Glutaminase

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Two important reactions are involved in fixing ammonia back to amino acids: 1.Reductive Amination: 2.Amino Transferases: All non-essential amino acids except for tyrosine and cysteine are derived and are dependent on transamination from glutamate.

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1. Reductive Amination : Alpha keto glutarate + Ammonia Glutamate NAD(P)HNAD(P) 2. Transamination reaction: Amino acid-1 Alpha keto acid-1 Amino acid-2Alpha keto acid-2 Transaminase Glutamate dehydrogenase PLP

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Well balanced polarity (Quite uncharged because of amide nitrogen yet sufficiently soluble in plasma No transporter required ) Non-Toxic AMMONIA ASPARTATE

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UREA BIOSYNTHESIS IS DIVIDED INTO 4 STAGES:- 1. TRANSAMINATION 2. OXIDATIVE DEAMINATION 3. AMMONIA TRANSPORT 4. REACTIONS OF THE UREA CYCLE

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DEF :- THE TRANSFER OF THE ALPHA-AMINO GROUP FROM ONE AMINO ACID TO A KETO ACID, RESULTING IN FORMATION OF A NEW AMINO ACID AND CORRESPONDING KETO ACID. E.G :- REACTION CATALYZED BY ALANINE AMINOTRANSFERASE ALANINE PYRUVATE (AMINO ACID ) (CORRESPONDING KETO ACID ) -KETOGLUTARATE GLUTAMATE (KETO ACID )(NEW AMINO ACID)

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KA AA Corresponding KA New AA TRANSAMINATION

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Aminoacids: 1.Transamination 2.Deamination 3.Transulfuration 4.Glutaminase 5.Gastrointestinal tract bacteria Degradation of Amino sugars Monoamine Oxidase Pyrimidine catabolism

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Nitrogen part is toxic. Excreted in the form of either : 1.Ammonia charged and alkaline. Excreted as ammonium ion in urine (3%) 2.Urea Neutral molecule Non toxic ( 80-85%) 3.Creatinine (3-4%) constant in urine ( 1% of Creatine every day) 4.Uric acid from Purines only !

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Inter organ exchange of amino acids

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The Glucose alanine cycle

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Amino acid catabolism in various tissues: 1.Intestines: predominantly use glutamine and asparagine for energy. 2. Liver : based on the blood levels of Glutamine (starvation / anabolism) produces Urea or proteins Cannot metabolize branched chain amino acids 3.Muscle: breaks down branched chain amino acids Produces Alanine transport form of ammonia to liver Produces glutamine to the kidneys.

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Kaplan lecture notes USMLE step 1

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Very important NH 3 removal mechanism ( esp BRAIN)

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` Kaplan lecture notes USMLE step 1 WHY ALANINE ? NOT GLUTAMATE DIRECTLY 2 ND NITROGEN 1 ST NITROGEN (AST) (ALT)

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Aminoacids: 1.Transamination 2.Deamination 3.Transulfuration 4.Glutaminase 5.Gastrointestinal tract bacteria Degradation of Amino sugars Monoamine Oxidase Pyrimidine catabolism

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Nitrogen is Excreted in the form of either : 1.Ammonia charged and alkaline. Excreted as ammonium ion in urine (3%) 2.Urea Neutral molecule Non toxic ( 80-85%) 3.Creatinine (3-4%) constant in urine ( 1% of Creatine every day) 4.Uric acid from Purines only !

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Inter organ exchange of amino acids in post absorptive state (FASTING)

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Inter organ exchange of amino acids in absorptive state (after feeding)

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The Glucose alanine cycle ALT (Transamination)

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Well balanced polarity (Quite non polar because of amide nitrogen yet sufficiently soluble in plasma No transporter required ) Non-Toxic AMMONIA ASPARTATE

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Ammonia + Bicarbonate + ATP Carbomyl Phosphate Citrulline Arginosuccinate Arginine CPS -1 Ornithine Transcarbomylase Arginosuccinate synthase Arginosuccinate Lyase Arginase Ornithine Aspartate NAG N-acetyl Glutamate High protein Diet Cytoplasm Mitochondria Fumarate Urea activator TCA cycle Oxaloacetate

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Acetyl Co-A + GlutamateN-acetyl Glutamate N-acetyl glutamate synthase (NAGS) (NAG) N-acetyl glutamate is the allosteric activator of Carbomyl phosphate synthase-1. Arginine

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Urea cycle disorders Hyperammonemia Encephalopathy Respiratory alkalosis VOMITING AVOIDANCE OF HIGH PROTEIN FOODS INTERMITTENT ATAXIA LETHARGY SEVERE MENTAL RETARDATION

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Symptoms of AMMONIA toxicity Tremor ( Correlate flapping tremor later on with Liver failure in Clinical medicine ) Slurred Speech Blurred Vision COMA Death

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Hyperammonemia type -1 Autosomal recessive Defect in CPS- 1 1 in 200,000 No orotic aciduria Cerebral Oedema, coma and death. Hyperammonemia type -2 X-linked recessive Defect in OTC MC urea cycle defect Orotic aciduria present Cerebral oedema, coma and death. CAUSE OF OROTIC ACIDURIA Increased Carbamoyl phosphate spills out from mitochondia to cytosol Pyrimidine synthesis Orotic acid Usmle!

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3. Citrullinemia : Defect in arginosuccinate synthase Citrullinuria Autosomal recessive 4. Arginosuccinic aciduria: Defect in arginosuccinate lyase Arginosuccinic acid blood, CSF, Urine 5. Hyperargininemia : Diet without arginine Defect in arginase enzyme

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Limit protein intake Decrease bacterial source of ammonia Antibiotics (Like Neomycin, Azithromycin) and Lactulose (purgative ) Replace intermediates of urea cycle Arginine Citrulline, Aspartate Remove excess ammonia Hemodialysis, sodium benzoate, phenyl acetate Very Important

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Lactulose Acidification conversion to NH4+ and induction of Purgation Mainstay Gut sterilization :-Neomycin/Azithromycin other antibiotics Very Important Combination of Sodium benzoate and Phenylacetate/Phenylbutyrate Sodium benzoate + Glycine Hippuric acid excreted Phenylacetate phenylacetyl glutamine excreted. (Phenylacetate conjugates with glutamine to form phenylacetylglutamine, which is excreted by the kidneys) Rarely used

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Source http://biocadmin.otago.ac.nz

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MCQ 1 Select the CORRECT answer. The first reaction in the degradation of the majority of common amino acids involves participation of : A.NAD + B.Pyridoxal Phosphate C.Thiamine Pyrophosphate(TPP) D.FAD E.NAD and TPP

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MCQ 2 After thorough investigations a man is diagnosed with orotic aciduria. To find out the cause of orotic aciduria which of the following investigations will you prefer? A. ALP levels B. vitamin b12 assay C. FIGLU excretion assay D. Peripheral smear E. serum bilirubin

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