Transcript Kim Biol 12 Metabolisme Aa dan asam nukleat
METABOLISME ASAM AMINO
KIMIA BIOLOGIS 2011
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.
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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%
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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
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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.
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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
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How much protein do we need?
•
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. ALLOWANCE FOR PROTEIN AGE Infants (0-1) Children (1-10) g/kg ~2.2 1.8 - 1.25
g/day 6.5-20 20- 38 Teens (11-18) 1.0 - 0.8
45-55 Adults (male) (female) 0.8
0.8
56 44 Pregnant or lactating - 20 - 30% more Athletes 1.2 -1.7
REQUIREMENT OF PROTEIN FROM DIFFERENT SOURCES (g/day for 70 kg human) Meat/fish/eggs/milk Non-vegetarian mixed diet Mixed vegetables Single vegetable* ~ 20-25 ~ 25-30 ~ 30-35 up to 75 * Except for soybeans
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PROTEIN AND AMINO ACID METABOLISM
dietary protein
Nitrogen balance
digestion amino acids other N compounds endogenous proteins a-ketoacids, NH glucose, lipids energy urea 3
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) Nitrogen excretion 8
PROTEIN AND AMINO ACID METABOLISM
dietary protein
DIGESTION
amino acids other N compounds endogenous proteins
TRANSLATION
a-ketoacids, NH glucose, lipids energy urea 3
Dietary protein is first hydrolyzed to amino acids, then rebuilt into endogenous protein by translation.
Nitrogen excretion 9
Digestion
•
Mouth
: accessible.
chewing, degradation of starch by amylase make proteins more •
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.
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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. 11
Protein and amino acid metabolism
dietary protein endogenous proteins amino acids
PROTEIN TURNOVER
a-ketoacids, NH 3 other N compounds glucose, lipids energy urea Nitrogen excretion 12
Siklus Nitrogen
Katabolisme Protein
Sumber
: diet, degradasi protein dalam tubuh Protein dicerna terlebih dahulu sebelum absorbsi Proses cerna usus halus : mulut, lambung, pankreas, dan Pencerna enzim protease : asam lambung dan berbagai Hasil akhir : asam amino bebas
Transport
: berbagai cara; memerlukan energi atau tidak memerlukan energi
Pencernaan Protein
Protein Diet Protein Tubuh Sintesis Protein: Asam amino nonesensial Protein baru (struktural, enzim, hormon) Pool Asam Amino NH3 Siklus Urea Urea Senyawa nitrogen lain: Heme, Purin, Pirimidin, dan Kreatin Asam Keto Siklus Krebs CO2 + H2O + ATP
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 badan keton
Amino Rangka karbon Siklus Urea Asam amino Glukosa Keton Asetil KoA CO2 UREA
Katabolisme Asam Amino
Transaminasi:
transfer gugus amino
ke asam α ketoglutarat menghasilkan asam glutamat
Deaminasi Oksidatif:
Pemecahan Glutamat menjadi amonia dan regenerasi α-ketoglutarat
Membutuhkan enzim dehidrogenase glutamat
α-ketoglutarat digunakan kembali reaksi transaminasi dalam
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
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 H 2 O) → ornitin
urea
dan
3 4 5 2 1
Siklus Urea dan Siklus Krebs berkaitan
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, dan oxaloasetat
Alanin, Sistein, Glisin, Treonin, Triptofan, Serin
Glukosa
Asparagin, Aspartat Aspartat, fenilalanin, Tirosin Isoleusin, Metionin, Valin Isoleusin, Leusin, Lisin, Treonin Asetoasetat Leusin, Lisin, Fenilalanin, Triptofan, Tirosin Arginin, Glutamat, Glutamin, Histidin, Prolin
AA esensial
Arginin Fenilalanin Histidin Isoleusin
Leusin Lisin
Metionin Treonin Triptofan Valin
Degradasi menjadi
α-ketoglutarat Fumarat, asetoasetil-KoA α-ketoglutarat Suksinil-KoA, asetil-KoA Asetil-KoA, asetoasetil-KoA Asetoasetil-KoA Suksinil-KoA Suksinil-KoA, piruvat Piruvat, asetil-KoA, asetoasetil KoA Suksinil-KoA
Keto Gluko
√ √ √ √ √ √ √ √ √ √ √ √ √
AA non esensial
Alanin Asparagin Aspartat Glisin Glutamat Glutamin Prolin Serin Sistein Tirosin
Degradasi menjadi
Piruvat Oksaloasetat Oksaloasetat, fumarat Piruvat α-ketoglutarat α-ketoglutarat α-ketoglutarat Piruvat Piruvat Asetoasetil-KoA , fumarat
Keto Gluko
√ √ √ √ √ √ √ √ √ √ √
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
: O 2 H 2 O Tirosin Fenilalanin hidroksilase
PKU (PhenylKetonUria) : Lack of Phenylalanine hidroxylase
*Asam amino esensial
Asam amino yang berasal dari 3 Fosfogliserat: Serin Sistein Glisin
Asam amino yang berasal dari aspartat: Lisin Metionin Treonin
Asam amino yang berasal dari piruvat: Leusin Isoleusin Valin
Asam amino aromatis: Tirosin Fenilalanin Triptofan
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)
Sintesis Histidin
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
Biosintesis Porfirin - The fundamental unit of porphyrins is -aminolevulinate (ALA) - Made by the pyroxidal phosphate (PLP) dependent enzyme aminolevulinate synthase PLP (vitamin B 6 )
Biosintesis Porfirin - We then combine 2 ALA into Porphobilinogen Ring close via Schiff Base
Biosintesis Porfirin dari PBG - Porphyrins are composed of 4 PBG subunits - The difference between Uroporphyrinogen I and III
METABOLISME NUKLEOTIDA
Metabolisme Nukleotida (nukleosida trifosfat)
Nukleotida : Senyawa ester fosfat dari suatu gula pentosa dengan basa nitrogen yang terikat pada atom C1 dari pentosa Basa : Purin (Adenin, Guanin) ; Pirimidin (Urasil, Timin, Sitosin) Gula : Ribosa (RNA), Deoksi ribosa (DNA) Unit monomer asam nukleat yang berfungsi sebagai prekursor dan fungsi biokimia lainnya contoh : AMP, GMP, UMP, TMP, CMP
Katabolisme Nukleotida
Asam nukleat (DNA dan RNA) dari diet didegradasi menjadi nukleotida oleh nuklease pankreas dan fosfodiesterase usus halus Nukleotida didegradasi menjadi nukleosida nukleotidase dan nukleosida fosfatase oleh Nukleosida diserap langsung Degradasi lanjutan Nukleosida + H 2 O basa + ribosa (nukleosidase) Nukleosida + P i basa + r-1-fosfate (n. fosforilase)
Katabolisme Purin (Adenin dan Guanin): 90% digunakan kembali (salvage) mamalia) (pada 10% didegradasi menjadi asam urat Basa
adenin
→ inosin → deaminase, nukleosidase
hipoksantin
; adenosin
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
Katabolisme Pirimidin (Sitosin, Timin, Urasil): Reaksi : defosforilasilasi, deaminasi, dan pemutusan ikatan glikosida.
Urasil dan timin Produk akhir : ß-alanina direduksi (dari sitosin dan urasil) ß-aminoisobutirat (dari timin) di hati
Biosintesis Nukleotida
Biosintesis purin (Adenin dan Guanin) o o Jalur
de novo → dari prekursor sederhana
Jalur
salvage → dari hasil degradasinya
Biosintesis Pirimidin (Sitosin, Urasil, dan Timin)
Biosintesis Purin jalur de novo Diawali dengan sintesis MonoPhosphate) IMP (Inosin Terbuat dari 6 prekursor sederhana ( CO2 ; Glisin ; 2 Format ; Glutamin ; dan Aspartat ) Sintesis IMP terdiri dari 11 tahapan reaksi
11 tahapan Reaksi Sintesis IMP
1.
2.
3.
4.
5.
Aktivasi ribosa-5-fosfat Penambahan glutamin → atom N9 Penambahan glisin → C4, C5, dan N7 Penambahan format → C8 Penambahan glutamin → N3 6.
7.
8.
Pembentukan cincin imidazola Penambahan bikarbonat → C6 Penambahan aspartat → N1 9.
Eliminasi fumarat 10.
Penambahan format → C2 11.
Siklisasi IMP
Sintesis AMP dan GMP
1.
2.
Adenilosuksinat sintase Adenilosuksinase 3.
4.
IMP dehidrogenase Transamidinase
AMPs IMP 1 2 AMP 3 XMP 4 GMP
Regulasi sintesis Purin
Biosintesis Purin jalur salvage Penggunaan ulang hasil degradasi nukleotida menjadi nukleotida Memerlukan energi yang lebih rendah daripada sintesis de novo Memerlukan 2 enzim penting
HGPRT (hipoksantin-guanin fosforibosil transferase)
APRT (Adenin fosforibosil transferase)
Jalur salvage Adenin
Jalur salvage Guanin
Biosintesis Pirimidin
Diawali dengan sintesis UMP (Uridin MonoPhosphate) Terbuat dari 3 prekursor sederhana ( HCO3 ; Aspartat ; dan glutamat ) Sintesis UMP terdiri dari 6 tahapan reaksi
Sintesis UTP Sintesis CTP
E. coli Manusia dan hewan