Metabolisme asam amino Kimia Biologis 2011

1. Metabolisme asam aminoKimia Biologis 2011

2. Inadequate dietary protein is still a major world problem Two-year old child with kwashiorkor, before and two weeks after start of treatment with good protein. Which is before and which is after? KWASHIORKOR - protein deficiency but adequate calories. Described in 1930s as “sickness of older child when new baby is born”, in language of Ga tribe of gold coast (now Ghana). Characteristic edema.

3. Protein malnutrition, continued FAMINE EDEMA Cause: inadequate synthesis of plasma proteins, especially albumin, so that osmotic pressure is not maintained and fluid escapes into tissues. Body water in extracellular space is increased relative to body weight. Extracellular water: Normal ~23.5% Kwashiokor ~30%

4. Protein malnutrition, continued Protein-Energy Malnutrition, Aka Marasmus, Protein-Calorie Deficiency, starvation. Other nutrients (vitamins and minerals) are also likely to be deficient. Starvation is usually the result of war, civil strife, drought, locusts. It especially affects infants and children; growth is slowed, infections and other diseases are common. NY Times, 4/17/00 Ethiopian child

5. Protein malnutrition, continued • Such extreme forms of malnutrition are rare in US, but protein deficiency can occur among: • Pregnant and lactating women, unless they increase their protein intake. • Individuals with eating disorders (bulimia, anorexia). • Elderly and chronically ill individuals who have lost interest in eating. • Chronic alcoholics and substance abusers. • Hospital patients with major protein needs and limited capacity for intake (e.g, post-surgery, severe burn victims). • Patients with genetic disorders in amino acid absorption or metabolism.

6. Dietary protein is the source of essential amino acids Dietary proteins provide the amino acids that humans cannot synthesize - the “essential” amino acids. The “non-essential” amino acids can be synthesized endogenously from intermediates of glycolysis or the TCA cycle. Essential Arginine (for children only) Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine Non-essential Alanine Asparagine Aspartate Cysteine Glutamate Glutamine Glycine Proline Serine Tyrosine Mnemonic for essential amino acids: PVT TIM HALL

7. In contrast to fat and glucose, there is no significant storage pool for amino acids; we must consume protein daily. • Requirement for protein depends on age, sex, activity. • Proteins differ in content of essential amino acids as well as digestibility. Diets that rely on a single source of protein may be out of balance with our nutritional needs. REQUIREMENT OF PROTEIN FROM DIFFERENT SOURCES ( g/day for 70 kg human) Meat/fish/eggs/milk ~ 20-25 Non-vegetarian ~ 25-30 mixed diet Mixed vegetables ~ 30-35 Single vegetable* up to 75 * Except for soybeans How much protein do we need?

8. Nitrogen balance dietary protein digestion In N balance excretion = intake (healthy adult) Positive N balance excretion < intake (growth, pregnancy, tissue repair) Negative N balance excretion > intake (malnutrition, starvation illness, surgery, burns) endogenous proteins amino acids a-ketoacids, NH3 other N compounds urea glucose, lipids energy Nitrogen excretion PROTEIN AND AMINO ACID METABOLISM

9. dietary protein endogenous proteins DIGESTION TRANSLATION amino acids a-ketoacids, NH3 other N compounds urea glucose, lipids energy Nitrogen excretion PROTEIN AND AMINO ACID METABOLISM Dietary protein is first hydrolyzed to amino acids, then rebuilt into endogenous protein by translation.

10. Digestion • Mouth: chewing, degradation of starch by amylase make proteins more accessible. • Stomach: acid pH denatures proteins; activates pepsinogen to cleave itself to pepsin, which initiates proteolysis. • Pancreas (exocrine): secretion of trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase (inactive proenzymes) • Duodenum: peptides from pepsin action stimulate release of cholecystekinin (pancreozymin). Cholecystekinin stimulates release of pancreatic pro-enzymes and of enteropeptidase, a protease secreted by cells of the duodenum.

11. Digestion • Duodenum: enteropeptidase activates trypsinogen to trypsin. Trypsin activates the other proteases, each of which has different specificity. Dietary proteins converted to peptides and free amino acids. • Small intestine: larger peptides are degraded on the surface of intestinal epithelial cells, which absorb amino acids and small (di- and tri-) peptides. Cytoplasmic peptidases complete conversion of peptides to amino acids, which can enter the circulation.

12. dietary protein endogenous proteins amino acids a-ketoacids, NH3 other N compounds urea glucose, lipids energy Nitrogen excretion Protein and amino acid metabolism PROTEIN TURNOVER

13. Siklus Nitrogen

14. Katabolisme Protein • Sumber : diet, degradasi protein dalam tubuh • Protein dicerna terlebih dahulu sebelum absorbsi • Proses cerna : mulut, lambung, pankreas, dan usus halus • Pencerna : asam lambung dan berbagai enzim protease • Hasil akhir : asam amino bebas • Transport : berbagai cara; memerlukan energi atau tidak memerlukan energi

15. Pencernaan Protein

16. Protein Diet ProteinTubuh Pool Asam Amino Siklus Urea Urea NH3 Sintesis Protein: Asam amino nonesensial Protein baru (struktural, enzim, hormon) Siklus Krebs CO2 + H2O + ATP Asam Keto Senyawa nitrogen lain: Heme, Purin, Pirimidin, dan Kreatin

17. Metabolisme Asam Amino • Lokasi: intraselular • Tahapan: • Pelepasan gugus α-amino (transaminasi & deaminasi oksidatif) • Gugus amino digunakan untuk biosintesis asam amino, nukleotida, dll; atau disekresikan dalam bentuk urea (siklus urea) • Asam α-keto (rangka karbon) dipecah menjadi senyawa lain: glukosa, CO2, asetil Ko-A, atau badanketon

18. Katabolisme Asam Amino Rangka karbon Amino Asam amino Siklus Urea Glukosa Keton Asetil-KoA CO2 UREA

19. Transaminasi: transfer gugus amino ke asam α-ketoglutarat menghasilkan asam glutamat

20. Deaminasi Oksidatif: • Pemecahan Glutamat menjadi amonia dan regenerasi α-ketoglutarat • Membutuhkan enzim glutamat dehidrogenase • α-ketoglutarat digunakan kembali dalam reaksi transaminasi

22. Siklus Urea Amonia hasil dari pemecahan glutamat digunakan untuk sintesis asam amino baru, sintesis nukleotida, atau senyawa amino lain (porfirin, dll) Amonia berlebih diekskresikan dalam bentuk urea (pada primata) melalui siklus urea

23. Reaksi siklus urea 1 : Karbamoil fosfat sintase 1 kondensasi CO2 dengan amonia → karbamoil fosfat 2 : Ornitin transkarbamoilase kondensasi ornitin dengan karbamoil fosfat → sitrulin 3 : Argininosuksinat sintetase Kondensasi sitrulin dengan aspartat → argininosuksinat 4 : Argininosuksinase Pemecahan argininosuksinat → fumarat dan arginin 5 : Arginase Pemecahan arginin (dengan bantuan H2O)→urea dan ornitin

24. 4 5 3 2 1

25. Siklus Urea dan Siklus Krebs berkaitan

26. Katabolisme rangka karbon asam amino • Rangka karbon 20 asam amino mengalami metabolisme lanjut yang berbeda • Terdiri dari 2 kelompok besar • Ketogenik: didegradasi menjadi senyawa antara metabolisme asam lemak; asetil-KoA atau asetoasetat • Glukogenik: didegradasi menjadi senyawa antara glikolisis atau SAS; piruvat, α-ketoglutarat, Suksinil-CoA, Fumarat, danoxaloasetat

27. Alanin, Sistein, Glisin, Treonin, Triptofan, Serin Isoleusin, Leusin, Lisin, Treonin Glukosa Asetoasetat Asparagin, Aspartat Leusin, Lisin, Fenilalanin, Triptofan, Tirosin Aspartat, fenilalanin, Tirosin Isoleusin, Metionin, Valin Arginin, Glutamat, Glutamin, Histidin, Prolin

30. Biosintesis Asam Amino Fenilalanin • Semua asam amino disintesis dari senyawa antara, kecuali tirosin disintesis dari asam amino esensial fenilalanin • Asam amino esensial: untuk sintesis protein, tidak dapat dibuat sendiri oleh tubuh, terdapat pada makanan • Asam amino non esensial : dapat dibuat oleh tubuh O2 Fenilalanin hidroksilase H2O Tirosin PKU (PhenylKetonUria) : Lack of Phenylalanine hidroxylase

31. *Asam amino esensial

34. Asam amino yang berasal dari 3-Fosfogliserat: Serin Sistein Glisin

35. Asam amino yang berasal dari aspartat: Lisin Metionin Treonin Aspartokinase (we don’t have this)

36. Asam amino yang berasal dari piruvat: Leusin Isoleusin Valin

37. Asam amino aromatis: Tirosin Fenilalanin Triptofan

38. Chorismate: Prekursor Asam Amino Aromatis - There is a single precursor for all ‘standard’ aromatic amino acids - Made from PEP! - From the Pentose Phosphate Pathway (an alternative to glycolysis)

39. Sintesis Histidin

40. Biosintesis Heme - In addition to proteins, some amino acids are used to make co-factors and signaling molecules: - Porphyrins, for example, are made from Succinyl CoA and Glycine

41. Biosintesis Porfirin - The fundamental unit of porphyrins is -aminolevulinate (ALA) - Made by the pyroxidal phosphate (PLP) dependent enzyme -aminolevulinate synthase PLP (vitamin B6)

42. Biosintesis Porfirin - We then combine 2 ALA into Porphobilinogen Ring close via Schiff Base

43. Biosintesis Porfirin dari PBG - Porphyrins are composed of 4 PBG subunits - The difference between Uroporphyrinogen I and III

44. Metabolisme nukleotida

45. Metabolisme Nukleotida (nukleosida trifosfat) • Nukleotida: Senyawa ester fosfat dari suatu gulapentosa dengan basa nitrogenyang terikat pada atom C1 dari pentosa • Basa : Purin (Adenin, Guanin) ; Pirimidin (Urasil, Timin, Sitosin) • Gula : Ribosa (RNA), Deoksi ribosa (DNA) • Unit monomer yang berfungsi sebagai prekursor asam nukleat dan fungsi biokimia lainnya contoh : AMP, GMP, UMP, TMP, CMP

46. Katabolisme Nukleotida • Asam nukleat (DNA dan RNA) dari diet didegradasi menjadi nukleotida oleh nuklease pankreas dan fosfodiesterase usus halus • Nukleotida didegradasi menjadi nukleosida oleh nukleotidase dan nukleosida fosfatase • Nukleosida diserap langsung • Degradasi lanjutan • Nukleosida + H2O  basa + ribosa (nukleosidase) • Nukleosida + Pi  basa + r-1-fosfate (n. fosforilase)

47. Purin Pirimidin

48. Katabolisme Purin (Adenin dan Guanin): • 90% digunakan kembali (salvage) (pada mamalia) • 10% didegradasi menjadi asam urat • Basa adenin→ inosin →hipoksantin; adenosin deaminase, nukleosidase

50. Asam urat pada beberapa jenis hewan didegradasi lebih lanjut Berbeda antar beberapa golongan hewan • Asam urat → primata, burung, reptil, serangga • Alantoin → mamalia lain • Asam alantoat → ikan • Urea → ikan bertulang rawan dan amfibi • Amonia → invertebrata laut