The document summarizes the metabolism of various amino acids. It notes that some amino acids are glucogenic, producing pyruvate or TCA cycle intermediates, while others are ketogenic, producing acetyl-CoA or acetoacetate. Key points include: - Alanine can be readily formed from pyruvate via transamination and is important for gluconeogenesis. - Arginine produces ornithine and urea and is the precursor for nitric oxide and creatine synthesis. - Serine can be converted to glycine and provides one-carbon units via tetrahydrofolate. Its carbon skeleton feeds into other amino acids. - Glutamate is central to amino acid

1. Metabolism of amino acids  Department of Biochemistry (J.D.) 2011

2. Glucogenic (13)  pyruvate and/or CAC intermediates Ketogenic (2) = Leu , Lys  acetyl-CoA + acetoacetate Mixed (5) = Thr, Ile, Phe, Tyr, Trp Intermediates of amino acid catabolism

3. Asp Ser, Gly, Thr, Ala, Cys, Trp Intermediates of amino acid catabolism pyruvate glucose fumarate succinyl-CoA 2-oxoglutarate oxaloacetate acetoacetate

4. Transamination of alanine alanine aminotransferase Alanine alanine pyruvate 2-oxoglutarate glutamate

5. Glu c os e -alanin e cy cle liver muscle glu c os e pyruv ate alanin e glu cose pyruv ate alanin e transamina tion gly colysis transamina tion glu c oneogene sis transport in blood alanine is non-toxic transport of ammonia from muscles to liver in the liver, alanine is the substrate for gluconeogenesis

6. Alanine - summary readily made from pyruvate (transamination) ALT is clinically important enzyme, mainly in liver, elevated catalytic concentration in blood serum – liver diseases Ala is released to blood mainly from muscles, together with Gln (postresorp tion phase) semiessential AA (in metabolic stress) – important substrate for gluconeogenesis

7. Hydrolysis of arginine  urea Arginine glutamate n o transamina tion arginine ornithine

8. NO is signal molecule from arginine BH 4 Exogenous NO sources glycerol trinitrate isosorbide dinitrate amyl nitrite isobutyl nitrite sodium nitroprusside citrulline N-hydroxyarginine nitric oxide radical

9. Synthesis of creatine (1. part) glycin arginine ornithine guanidinoacetate from Greek κρέας (meat) glycine

10. Synthesis of creatine (2. part) N 1 -methylation of guanidinoacetate S-adenosylmethionine (SAM) S-adenosylhomocysteine creatine N -methylguanidine- N -acetate guanidinoacetate

11. N 2 -Phosforylation of creatine kreatin kreatinfosfát ATP creatine creatine phosphate

12. Creatinine is a catabolite of creatine made in non-enzymatic reaction non-enzymatic cyclization dehydratation kreatin creatinine - H 2 O creatine

13. Arginine - summery semiessential AA (childhood) the most basic AA (guanidine, p K B = 0.5) no transamination , Arg releases ornithine + urea Arg + Gly + Met  creatine releases NO (vasodilator) OTC (over-the-counter) preparations in pharmacy

14. Dehydratation + deamination of serine Serine pyruvate imine enamine

15. Conversion of serine to glycine H 2 O + N 5 N 10 -CH 2 -FH 4 methylene FH 4 serine glycine cofactor: tetrahydrofolate (FH 4 )

16. Transamination of serine and glucose formation reverse reaction: synthesis of serine pathway is different - through ph os ph oserin e serine hydroxypyruvate glycerate 3-P-glycerate glucose 2-oxoglutarate

17. Betain e is made by cholin e oxidation oxida tion De c arboxyla tion of serin e gives ethanolamin e. Methyla tion of ethanolamin e leads to cholin e de c arboxyla tion methyla tion serin e ethanolamin e cholin e betain e cholin e

18. Serine - summary non-essential glucogenic AA source of C1 fragments ( attached to tetrahydrofolate ) component of glycerophospholipids d e c arboxyla tion gives ethanolamin e  cholin e carbon skeleton used for selenocystein e serine side chain in proteins: the site of phosphorylation the linkage of oligosaccharides ( O -glycoside bond) nucleophilic -OH group in a c tiv e site of enzym e (serine proteases)

19. The complete catabolism of glycine C1 fragment (methylene) is transferred to tetrahydrofolate Glycine C O O H C H 2 N H 2 N 5 N 1 0 C H 2 F H 4 + + C O 2 N H 3 F H 4 +

20. Oxidative deamination of glycine glyoxylate oxalate

21. Oxal ate in human body 60 % c atabolism of glycin e and ethanolamin e 30 % c atabolism of vitamin C 10 % food ( spinach , r hubarb , mangold, tea , cocoa )

22. Glycine - summary Catabolism complete oxidation to CO 2 + NH 3 oxidative deamination to oxalate Anabolic conversions donor of C1 fragment serine porphyrines purine bases creatine glutathione (GSH) conjugation agent (bile acids, xenobiotics)

23. Threonine (4C) is split to glycine (2C) and acetaldehyde (2C) Threonine essential AA two asymmetric C atoms the site of phosphorylation and glycosylation in proteins n o transamina tion glycine pyruvate serine acetaldehyde

24. Methionine is methyl ation agent ( homocystein e side product) B 12 ethanolamin e noradrenalin e guanidinace tate methionine S-adenosylmethionine substrate substrate- CH 3 choline adrenalin e creatine homocysteine remethylation Methionine n o transamina tion

25. S -Adenosylmethionine (SAM) contains tr ivalent positively charged s ulfur atom c ation - sulfonium

26. Cysteine is made from methionine methionine homocysteine cystathionine homoserine cysteine condensation with serine cysteine release pyridoxal-P B 12 succinyl-CoA

27. Methionine - summery essential AA, rather rare in foodstufs S-adenosylmethionine (SAM) is methylation agent metabolized to cysteine  Cys is non-essential AA C-skeleton of cysteine comes from serine, sulfur atom from methio ni ne final catabolite is succinyl-CoA (glucogenic)

28. Homocystein e is harmful mechanism of its action is not yet understood direct action on blood vessel epithelium decreases t h rombocyt e life and fibrinol ysis supports formation of oxygen radicals – damage of vessel wall increases LDL lipoperoxida tion elevated blood level of homocysteine is risk factor of cardiovascular diseases to eliminate homocysteine - three vitamins are needed: folate, cobalamine, pyridoxin

29. C ystein e catabolism: oxygenation of -SH group cysteine oxygenation cysteine sulfinate cysteic acid decarboxylation transamination hypotaurine taurine oxygenation sulfinylpyruvate Cysteine oxygenation

30. The formation of sulfite under physiol. pH – dissociation only to HSO 3 - sulfite sulfinylpyruvate hydrolytic cleavage of sulfite pyruvate

31. Sulfite oxidase catalyzes sulfate formation cysteine HSO 3 - + H 2 O  SO 4 2- + 3H + + 2e - blood pla s ma (0 . 5 mmol/l) acidify body fluids reduce molybdopterine PAPS urine

32. Distinguish anion S 2- (e.g. ZnS zinc sulfid e) Sulfid e in organic anion SO 4 2- Sulf ate R-S-R dialkylsulfid e Sulfid e organic anion SO 3 2- Sulfit e

33. Transamination of cysteine and sulfan e production CN - SCN - in smokers SO 4 2- sulfhemoglobin sign al mole c ul e ? 2-oxoglutarate cysteine glutamate mercaptopyruvate desulfuration pyruvate

34. Cysteine - summary both pathways go to pyruvate (glucogenic) main catabolism: sulfur oxygenation  sulfite  sulfate high protein diet leads to physiologic acidosis cystein provids taurine – conjugation agent (e.g. bile acids) taurine is semi e s sen tial AA in metabolic stre s s taurine is a component of „ energ y drinks“ cysteine – part of glutathione (GSH) - antioxidant d e c arboxyla tion of Cys – cysteamin e , in CoA-SH in proteins – disulfid e bonds (tertiary structure) cysteine proteases: active site contains –SH group

35. Six amino acids provide pyruvate 1. Serine – dehydratation + deamination 2. Glycine – via serine 3. Threonine – via glycine 4. Alanine – transamination (ALT) 5. Cysteine – both catabolic pathways 6. Tryptophan – via alanine (see later)

36. Transamination of Asp  oxaloacetate ( C AC) AST (aspartate aminotransferase) – clinically important enzyme in urea cycle, Asp donates one nitrogen into urea and releases fumarate decarboxylation of Asp  β -alanine (part of coenzyme A) donor of nitrogen in purine synt hesis ( fumar ate released) whole structure given for pyrimidin e bases synthesis a spartam (sweetener) condensation with ammonia  asparagine (for cell utilization, not as detoxi c a tion of am monia) Aspartate

37. β -Alanine is made by the decarboxylation of aspartate - CO 2 β α in the structure of CoA-SH

38. Glutamate with oxaloacetate afford aspartate (transamination) AST reaction produces aspartate for urea synthesis aspartate aminotransferase Glutamate oxaloacetate aspartate  urea glutamate 2-oxoglutarate

39. Dehydrogenative deamination of glutamate is the main producer of ammonia in tissues g lutamate dehydrogenase (GD, GDH, GMD) glutamate 2-iminoglutarate 2-oxoglutarate (CAC)

40. Decarboxylation of glutamate glutamate

41. Compare: GABA vs . GHB GABA GHB g ama- h ydroxy b utyrate, synthetic drug, liquid ecstasy, belongs to “date rape drugs “ , euphoria, sedation - CNS depressant, downer GHB g amma- a mino b utyric a cid, Inhibitory neurotransmitter in the brain, formed by decarboxylation of glutamate GABA

42. Chinese restaurant syndrome after ingestion of larger amounts of monosodium glutamate (MSG, E621) taste enhancer – e.g. instant soups, soya souce, etc. burning sensations, numbness, tingling, feelings of warmth, facial pressure or tightness, chest pain, headache, nausea, rapid heartbeat, bronchospasm in people with asthma, drowsiness, weakness ... MSG is not recommended for children

43. Glutamate - summary produced in the transaminations of most AA glutamate dehydrogenase reaction produces most ammonia in body transaminations are reversible, so glutamate can be converted to 2-oxoglutarate (glucogenic) Glu + NH 3  Gln (ammonia detoxification) glutamate is readily made from glutamine, histidine, proline, ornithine pure monosodium glutamate, flavour enhancer, can cause health problems (chinese restaurant syndrome)

44. Amino acids as neurotransmiter s Chlorid e channels (Cl - ) C ation ic channels (Na + ) GABA Glycin e Glutam ate Aspart ate (Acetylcholin e ) Inhibi tory Excita tion

45. See also the previous lecture (AA-1) glutamine synthesis is the way of ammonia detoxification in tissues including liver in kidneys, glutamine releases ammonia (deamidation) metabolic fuel for some tissues (enterocyt es , fibroblast s , lym ph ocyt es , ma c ro pha g es ) donor of nitrogen for syntheses (glu c osamin e , purin es ) Glutam in e

46. T hree amino acids donate four N atom s in purine bases synthesis fumar ate glutam ate aspartate glycine amide group of glutamine amide group of glutamine

47. Proline is converted to glutamate (and vice versa ) proline glutamate 5-semialdehyde glutamate pyrroline-5-carboxylate oxidation addition of H 2 O ring opening Proline n o transamina tion

48. Hydroxylation of proline with 2-oxoglutarate as reductant - CO 2 proline 2-oxoglutarate 4-hydroxyproline succinate Fe 2+ ascorbate

49. Proline - summary non-essential AA, can be formed from glutamate converted to glutamate (glucogenic) hydroxylation of proline in collagen is post-translation modification, requires ascorbate (vitamin C), Fe 2+ , and 2-oxoglutarate (unusual co-reductant) 4-hydroxyproline is catabolized to pyruvate (see Harper)

50. Ca tabolism of histidin e starts with desatura tion and deamination urocanic acid (urocanate) Histidine n o transamin ation

51. Urocanate cleavage affords C 1 fragment FIGLU urocanate N -formiminoglutamate (Figlu) glutamate addition of water oxidative ring splitting

52. Decarboxylation of histidine  histamine histidine decarboxylase occurs in mast cells and basophils histamine stimulates HCl production in stomach is released in allergic reactions triggers inflammatory response antihistaminics are drugs blocking the action of histamine - CO 2 histidine histamine

53. Histidine is responsible for buffering actions of proteins p K B = 8 p K A (His) = 6 p K A (His in proteins ) = 6-8

54. Histidine - summary semiessential AA no transamination, catabolism begins with desaturation and deamination the source of 1C groups (formimino) converted to glutamate (glucogenic) histidine is abundant in hemoglobin – buffer system post - transla tion modification: methyla tion of His in a c tin e /myosin e  3-methylhistidin e – its urine ex c re tion is the indicator of muscle proteol ysis and nutrition status

55. Leucine (1) - transamination + decarboxylation Leucine, Isoleucine, Valine (BCAA) branched 2-oxoacid oxidative decarboxylation branched acyl-CoA transamination

56. Leucine (2) - dehydrogenation 2,3-dehydrogenation branched unsaturated acyl

57. Leucine (3) – carboxylation at C4 carboxylation acyl of dicarboxylic branched unsaturated acid

58. Leucine (4) – hydratation of double bond

59. Leucine (5) – splitting the C-C bond in HMG-CoA HMG-CoA lyase acetoacetate

60. Compare the final products of BCAA B 12 B 12 glucogenic succinyl-CoA Valine ketogenic glucogenic acetyl-CoA + succinyl-CoA Isoleucine ketogenic acetyl-CoA + acetoacetate Leucine

61. BCAA - summery all BCAA are essential the first three reactions are the same (transamination, oxid. decarboxylation, dehydrogenation), final products are different leucine – ketogenic, valine – glucogenic, isoleucine – mixed after meal, BCAA make about 70 % of AA in blood, because the liver does not utilize them (lack of aminotransferases) BCAA are most utilized in muscles and brain BCAA infusion are applied in severe catabolic conditions

62. Lysine catabolism (1) Lysine n o transamina tion lysine 2-oxoglutarate ketimine (Schiff base)

63. Lysine catabolism (2) ketimine hydrogenation dehydrogenation saccharopine aldimine

64. Lysine catabolism (3) hydrolysis aldimine allysine glutamate

65. Lysine catabolism (4) allysine dehydrogenation 2-aminoadipate

66. Lysine catabolism (5) 2-aminoadipate 2-oxoglutarate transamination 2-oxoadipate glutamate

67. Lysine is the substrate for carnitine (the transfer of FA from cytosol to mitochondria) carnitine acylcarnitine

68. Cross-links in collagen hydrogenated aldimine lysine (lysyl residue in polypeptide) dehydrated aldol allysine allysine lysine + hydrogenation products of reaction between the amino groups in side chains of lysine with the modified lysine side chains comprising the aldehyde group (the result of oxidation of lysine to allysine ) – aldol type or aldimine type of cross-links.

69. Formation of fibrin clot during blood coagulation (cross-linking of fibrin) lysine glutamine cross-linking

70. Lysine - summary essential AA, no transamination ε -amino group is removed as glutamate  -amino group is removed from aminoadipate by transamination final product acetyl-CoA (ketogenic) Other conversions: lysin e in many proteins binds ubi qu itin ( targeting for proteasom e ) carnitine (transport system for FA to mitochondria) d e c arboxyla tion  c adaverin e in collagen: cross bridges, hydroxylation  hydroxylysin e in fibrin: cross linking during blood coagulation

71. Catabolism (1) Phenylalanine, Tyrosine hydroxylation transamination phenylalanine tyrosine p-hydroxyphenylpyruvate

72. Catabolism (2) p-hydroxy ph enylpyruv ate homogentisate (2,5-dihydroxyphenylacetate) oxidative decarboxylation rearrangement hydroxylation

73. Catabolism (3) oxidative cleavage of aromatic ring dioxygenase maleylacetoacetate

74. Catabolism (4) maleylacetoacetate fumarylacetoacetate isomeration

75. Catabolism (5) fumarylacetoacetate fumarate acetoacetate

76. Hyperphenylalaninemia and Phenylketonuria deficit of hydroxylase or BH 4 elevated blood Phe and its metabolites excretion of phenylpyruvate by urine phenylalanine tyrosine hydroxylase

77. Metabolites of phenylalanine phenylalanine phenylpyruvate transamination oxid. decarboxylation phenylacetate phenyllactate hydrogenation

78. if not treated properly – mental retardation and other problems treatment – low phenylalanine diet products containing sweetener aspartam must be avoided L-aspartyl-L-phenylalanine methyl ester - phenylalanine is released by hydrolysis: Hyperphenylalaninemia and Phenylketonuria

79. Hydroxylation of phenylalanine gives tyrosin e phenylalanine tyrosine c o - redu c tant tetrahydrobiopterin e

80. DOPA a nd dopamin e from tyrosine tyrosine dopamine (catecholamine) (3,4-dihydroxyphenylalanine) hydroxylation decarboxylation Tyrosine

81. Linguistic note abbreviation DOPA comes from older English nomenclature oxo group and hydroxyl group were not distinguished properly: DOPA = d i o xo p henyl a lanine correct chemical name is: 3-(3,4-dihydroxyphenyl)alanine

82. Two more catecholamines from dopamine Cu 2+ nor- = N -demethyl hydroxylation at C2 N -methylation dopamine noradrenaline adrenaline O 2 , ascorbate

83. Conversion of dopamine to melanin, a dark pigment of skin, hair, fur dopamine dopaquinone melanin multiple condensations

84. Conversion of tyrosin e to thyroxin e bound to thyreoglobulin tyrosine 3’,5’-diiododtyrosine thyroxine

85. Phenylalanine, tyrosine - summary Phe is essential amino acid, Tyr not Tyr is made by Phe hydroxyla tion ( tetrahydrobiopterin e cofactor) catabolism is the same for both AA (mixed AA) provide fumarate for CAC (glucogenic) acetoacetate (ketone body) tyrosine is converted to hormones (catecholamines, thyronines) and dark skin pigment melanin

86. Catabolism (1) O 2 Tryptophan n o transamina tion tryptophan oxidative cleavage of aromatic ring N -formylkynurenine

87. Catabolism (2) hydrolysis of amide group formamide hydroxylation formate

88. Catabolism (3) hydrolytic cleavage of alanine 3-hydroxyanthranilate

89. Catabolism (4) 3-hydroxyanthranilate nicotinamide 2-oxoadipate

90. Decarboxylation of tryptophan tryptophan tryptamine

91. Conversion of tryptophan to melatonin sleep-wake cycle the hormone of darkness Trp hydroxylation 5-hydroxytryptophan decarboxylation N -acetylation O -methylation

92. Tryptophan - summary essential AA complicated catabolism donor of 1C fragment (form ic acid - formate ) no transamination, amino group leaves as alanine (glucogenic) final product acetyl-CoA (ketogenic) source of nicotinamide and NAD + bacterial decomposition in large intestine  indole and skatole (3-methylindol e ) – exhibit strong fecal odor

93. Five vitamins are formed in the body, only four are utilized in tissues, from tryptophan large intestine ( ba cteria) large intestine ( ba cteria) skin, from cholesterol (UV radiation ) large intestine ( ba cteria) – n ot absorbed ! Niacin Biotin Ph yl l o quinone C alciol C obalamin e Where and how produced Vitamin

94. Seven amino acids do not undergo transamination ornithine 2-aminoadipate homoserine glycine alanine glutamate NH 3 (desaturation deamination) Arginine Lysine Methionine Threonine Tryptophan Proline Histidine  -NH 2 group is removed as Amino acid

95. pyruv ate  glu cose urea , NO, creatine ethanolamin e  cholin e  betain e ; donor of 1C fragment , selenocysteine hem e , c reatin e , GSH, c onjuga tion reagent ( e.g . gly c ochol ate ) donor of methyl, c reatin e , homocystein e, cysteine glutathione ( GSH ) , taurin e , SO 4 2- , PAPS, cysteamin e (CoA) d onor of -NH 2 (urea, pyrimidin es ), oxaloacetate, fumar ate , β -alanin e (CoA) NH 4 + , 2-oxoglutar ate , GABA , ornithine NH 4 + , d onor of -NH 2 (synt hesis of glu c osamin e , purin es ) glutamate, hydroxyprolin e glutamate, histamin e , donor of 1C fragment glutamate, allysin e ( collagen ), c arnitin e , c adaverin e fumar ate , c atecholamin es , thyroxin e , melanin s ni c otinamid e , serotonin, melatonin, donor of 1C fragment , indole, skatole Ala Arg Ser Gly Met Cys Asp Glu Gln Pro His Lys Tyr Trp Biochemic ally relevant produ c t A A