2Learning objectives: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 liverDescribe the urea cycle and the enzymes involved in production of urea in the liverDefine and classify Hyperammonemias . List the enzymes deficient in various hyperammonemias and its clinical features
3Catabolism of Amino acids Amino group – NH3Formation of ureaCarbon skeletons – Formation of Glucose and Ketone bodies.
4FATE OF THE CARBON SKELETONS Carbon skeletons are used for energyGlucogenic: TCA cycle intermediates or Pyruvate (Gluconeogenesis)Ketogenic: Acetyl CoA, Acetoacetyl CoA, or Acetoacetate
5DIGESTION AND ABSORPTION PROTEINSGastric juice ( acidity denatures proteins )Intestinal enzymes hydrolyzeAMINO ACIDSAmino acid transporters Na+Amino acid symporter (can take up di and tri peptides )UPTAKEDEFECTS :-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 cysteineUrinary stones .Cystine forms Cystine by disulfide linkage (less soluble Stones )
6Nitrogen BalanceDifference btw total nitrogen intake and total nitrogen loss in fecesPOSITIVE NITROGEN BALANCE – MORE NITROGEN INGESTION THAN LOSSGrowing infants and pregnant womenNORMAL BALANCE – INTAKE MATCHES OUTPUTNormal IndividualsNEGATIVE BALANCE – NITROGEN OUTPUT EXCEEDS INTAKEFollowing surgery , cancer , malnutrition (decreased protein intake )
7EXCESS AMINO ACIDS ARE DEGRADED NOT STORED OVERVIEW OF AMINO ACID METABOLISMENVIRONMENT ORGANISMBio-synthesisProteinIngestedprotein231RecyclingaAMINOACIDSbcDegradation(required)cPurinesPyrimidinesPorphyrinsNitrogenNH3CarbonskeletonsUrea(ketogenic)(glucogenic)pyruvateα-ketoglutaratesuccinyl-CoAfumarateoxaloacetateUsed forenergyacetoacetateacetyl CoA
9Why ammonia is toxic ? Affects central nervous system Alkalization of intracellular compartmentDisrupts oxidative phosphorylation ATP depletionIncreased glutamate in BrainDecreased Neurotransmitters – GABA – convulsionsCerebral edema
10Symptoms of AMMONIA toxicity Flapping Tremor (Asterixis)( Correlate flapping tremor later on with Liver failure in Clinical medicine )Slurred SpeechBlurred VisionCOMA Death
11Metabolic fates of ammonia Ammonotelic – FishesLots of water availableUricotelic – Reptiles and birdsBirds have to keep minimum body weight for flightUreotelic – Mammals
12Adults degrade 1-2% of body protein daily Body Proteins80-85%Amino acids25%CatabolismUREA
13Amino acids Sources of Amino Acids : Utilization of Amino acids: Exogenous – DietEndogenous –Breakdown of muscle proteinBiosynthesis from intermediates of citric acid cycle.Synthesis of New proteinsFormation of NucleotidesFormations of Porphyrins and CatecholaminesProduction of energy and Ammonia.
14Fate of Amino group1) Reutilization: Glutamate and Glutamine are involved in recycling of amino acids.ATPADPGlutamate + AmmoniaGlutamineGlutamine SynthaseThey 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 synthesisGlutamineGlutamate + AmmoniaGlutaminase
152. Formation of amino acids from carbon skeletons require ammonia Two important reactions are involved in fixing ammonia back to amino acids:Reductive Amination:Amino Transferases:All non-essential amino acids except for tyrosine and cysteine are derived and are dependent on transamination from glutamate.
17UREAWell balanced polarity (Quite uncharged because of amide nitrogen yet sufficiently soluble in plasma No transporter required )Non-ToxicAMMONIAASPARTATE
18CATABOLISM OF PROTEINS UREA BIOSYNTHESIS IS DIVIDED INTO 4 STAGES:-1. TRANSAMINATION2. OXIDATIVE DEAMINATION3. AMMONIA TRANSPORT4. REACTIONS OF THE UREA CYCLE
19TRANSAMINATIONDEF :- 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 AMINOTRANSFERASEALANINE PYRUVATE(AMINO ACID ) (CORRESPONDING KETO ACID )α-KETOGLUTARATE GLUTAMATE(KETO ACID ) (NEW AMINO ACID)ALTALL TRANSAMINASESREQUIRE PLP (VIT B6)PLP
21USES OF TRANSAMINATION FIRST STEP OF CATABOLISM OF PROTEINSSYNTHESIS OF NON-ESSENTIAL AMINO ACIDS and INTERCONVERSION OF AMINO ACIDSREGENERATION OF TCA CYCLE intermediates
22OVERALL FLOW OF NITROGEN IN AMINO ACID CATABOLISM
23Sources of ammonia in the body Aminoacids:TransaminationDeaminationTransulfurationGlutaminaseGastrointestinal tract bacteriaDegradation of Amino sugarsMonoamine OxidasePyrimidine catabolism
24Nitrogen metabolismNitrogen part is toxic. Excreted in the form of either :Ammonia – charged and alkaline. Excreted as ammonium ion in urine (3%)Urea – Neutral molecule – Non toxic –( 80-85%)Creatinine (3-4%) – constant in urine ( 1% of Creatine every day)Uric acid – from Purines only !
27Amino acid catabolism in various tissues: Intestines:predominantly use glutamine and asparagine for energy.Liver :based on the blood levels of Glutamine (starvation / anabolism) – produces Urea or proteinsCannot metabolize branched chain amino acidsMuscle:breaks down branched chain amino acidsProduces Alanine – transport form of ammonia to liverProduces glutamine – to the kidneys.
31Sources of ammonia in the body Aminoacids:TransaminationDeaminationTransulfurationGlutaminaseGastrointestinal tract bacteriaDegradation of Amino sugarsMonoamine OxidasePyrimidine catabolism
32Nitrogen metabolism Nitrogen is Excreted in the form of either : Ammonia – charged and alkaline. Excreted as ammonium ion in urine (3%)Urea – Neutral molecule – Non toxic –( 80-85%)Creatinine (3-4%) – constant in urine ( 1% of Creatine every day)Uric acid – from Purines only !
33Inter organ exchange of amino acids in post absorptive state (FASTING)
34Inter organ exchange of amino acids in absorptive state (after feeding)
35The Glucose alanine cycle ALT (Transamination)ALT (Transamination)
36UREAWell balanced polarity (Quite non polar because of amide nitrogen yet sufficiently soluble in plasma No transporter required )Non-ToxicAMMONIAASPARTATE
37Urea cycle Ammonia + Bicarbonate + ATP CPS -1 NAG – N-acetyl Glutamate High protein DietAmmonia + Bicarbonate + ATPCPS -1NAG – N-acetyl GlutamateactivatorCarbomyl PhosphateOrnithine TranscarbomylaseOrnithineCitrullineMitochondriaCytoplasmArginosuccinate synthaseAspartateOxaloacetateArginosuccinateArginosuccinate LyaseFumarateTCA cycleArginaseArginineUrea
39Production of NAG: Acetyl Co-A + Glutamate N-acetyl Glutamate N-acetyl glutamate synthase (NAGS)ArginineN-acetyl glutamate is the allosteric activator of Carbomyl phosphate synthase-1.
40Urea cycle disorders Hyperammonemia Encephalopathy Respiratory alkalosisVOMITINGAVOIDANCE OF HIGH PROTEIN FOODSINTERMITTENT ATAXIALETHARGYSEVERE MENTAL RETARDATION
41Symptoms of AMMONIA toxicity Tremor( Correlate flapping tremor later on with Liver failure in Clinical medicine )Slurred SpeechBlurred VisionCOMA Death
42Disorders of UREA cycle Usmle!Hyperammonemia type -1Hyperammonemia type -2X-linked recessiveDefect in OTCMC urea cycle defectOrotic aciduria presentCerebral oedema , coma and death.Autosomal recessiveDefect in CPS- 11 in 200,000No orotic aciduriaCerebral Oedema , coma and death .CAUSE OF OROTIC ACIDURIA Increased Carbamoyl phosphate spills out from mitochondia to cytosolPyrimidine synthesis Orotic acid
433. Citrullinemia :Defect in arginosuccinate synthaseCitrullinuriaAutosomal recessive4. Arginosuccinic aciduria:Defect in arginosuccinate lyaseArginosuccinic acid blood, CSF, Urine5. Hyperargininemia :Diet without arginineDefect in arginase enzyme
44Treatment of Hyperammonemia: Limit protein intakeDecrease bacterial source of ammonia – Antibiotics (Like Neomycin, Azithromycin)and Lactulose (purgative )Replace intermediates of urea cycle – Arginine Citrulline, AspartateRemove excess ammonia – Hemodialysis, sodium benzoate, phenyl acetateVery ImportantVery Important
45Drugs Combination of Sodium benzoate and Phenylacetate/Phenylbutyrate Lactulose – Acidification – conversion to NH4+ and induction of PurgationMainstayGut sterilization :-Neomycin/Azithromycin other antibioticsVery ImportantCombination of Sodium benzoate and Phenylacetate/PhenylbutyrateSodium benzoate + Glycine Hippuric acid excretedPhenylacetate phenylacetyl glutamine excreted. (Phenylacetate conjugates with glutamine to form phenylacetylglutamine, which is excreted by the kidneys)Rarely used
48MCQ 1 Select the CORRECT answer . The first reaction in the degradation of the majority of common amino –acids involves participation of :NAD +Pyridoxal PhosphateThiamine Pyrophosphate(TPP)FADNAD and TPP
49MCQ 2After 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 levelsB. vitamin b12 assayC. FIGLU excretion assayD. Peripheral smearE. serum bilirubin