03 - Metabolisme Protein - Monogastrik [PDF]

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Metabolisme Asam Amino pada Monogastrik Sri Suharti Departemen Ilmu Nutrisi dan Teknologi pakan



Fakultas Peternakan IPB 2016



Protein Degradation Protein Pepsin (stomach) Trypsin, chymotrypsin (pancreas) Peptides



Carboxypeptidase (pancreas) Aminopeptidase (small intestine) Amino Acids



Protein Digestion SMALL INTESTINE Trypsin, chymotrypsin break down polypeptides into peptides (both from pancreas) Carboxypeptidase (from pancreas) and aminopeptidase (from small intestine) break down peptides into amino acids



Chemistry of Digestion: Proteins Proteins



Small polypeptides Amino acids Endopeptidases (proteases) ◦E.g. pepsin (stomach) Exopeptidases ◦E.g. carboxypeptidase (small intestine)



Amino Acid Degradation In animals,amino acids undergo oxidative degradation in 3 different metabolic circumstances: 1. During normal synthesis and degradation of cellular proteins, some amino acids, that are not needed for new protein synthesis, undergo OXİDATİVE DEGRADATİON 2. When a diet is rich in protein, the surplus amino acids are catabolized ( in the liver amino acids can't be stored) 3. During starvation and uncontrolled DM, when carbohydrates are unavailable or improperly utilized, cellular proteins are used as fuel.



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Overview



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Animals convert α-amino nitrogen to varied end products as ammonia, uric acid or urea.



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Humans are ureotelic and excrete non-toxic, water-soluble urea.



Hasil akhir : 1. Organisme ureotelik urea (mamalia) 2. Organisme urikotelik asam urat (reptil & burung ) 3. Organisme ammonitelik ammonia (NH3)pd ikan



METABOLISME ASAM AMINO Asam amino yg terbentuk di usus akan diabsorbsi dan dibawa oleh peredaran darah ke dalam sel-sel tubuh. METABOLISME ASAM AMINO DI DALAM SEL : 1. KATABOLISME : * Katabolisme Nitrogen asam amino UREA * Katabolisme kerangka karbon asam amino senyawa amfibolik 2. ANABOLISME sintesis protein Ada 20 jenis asam amino dasar : 10 macam adalah asam amino essensial 3. PEMBENTUKAN PRODUK KHUSUS



ASAM AMINO PROTEIN



N



PRODUK KHUSUS



UREA



KERANGKA C



SENYAWA AMFIBOLIK ENERGI



BIOSINTESIS MENJADI SENYAWA LAIN



Apabila asam amino dr makanan berlebihan (melebihi kebutuhan tubuh untuk sintesis protein, produk khusus dll.)maka kelebihan/sisanya tak dapat ditimbun diubah menjadi lemak sebagai cadangan kalori tubuh



TAHAP KATABOLISME NITROGEN ASAM AMINO 1. TRANSAMINASI



2. DEAMINASI OKSIDATIF 3. TRANSPOR AMONIA 4. SIKLUS UREA



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Transamination Transamination transfers α-amino nitrogen to α-ketoglutarate, forming glutamate. Transamination interconverts pairs of α-amino acids and α-ketoacids. Amino acids that don't participate in transamination:Lysine, threonine, proline, hydroxyproline. Reversible Aminotransferases (transferases) remove the amino group from most amino acids and produce the corresponding α -ketoacid



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Cofactor:Pyridoxal phosphate Pyridoxamine is the intermediate in the reaction. Alanine-pyruvate amino transferase (alanine aminotransferase) and glutamate α-ketoglutarate amino transferase (glutamate aminotransferase) catalyze the transfer of amino groups to pyruvate (forming alanine) or to α-ketoglutare (forming glutamate)



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 Each aminotransferase is specific for one pair of substrates but nonspecific for the other.  Since alanine is also a substrate for glutamate aminotransferase, all the amino nitrogen from amino acids that undergo transamination can be concentrated in glutamate  The effect of transamination reaction is to collect the amino groups from many different amino acids in the form of L-glutamate.  L-glutamate then functions as an amino group donor for biosynthetic pathways or for excretion pathways that lead to the eliminaton of nitrogenous waste products.



 Glutamate releases its amino qroup as ammonia in the liver.  In hepatocytes, glutamate is transported from cytosol into mitochondria, where it undergoes OXİDATİVE DEAMİNATİON by glutamate dehydrogenase.



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Gambar : kaitan antara asam amino dengan siklus asam sitrat



Siklus Urea Gugus-gugus amin dilepaskan menjadi ion amonium (NH4+) yang selanjutnya masuk ke dalam siklus urea di hati. Dalam siklus ini dihasilkan urea yang selanjutnya dibuang melalui ginjal berupa urin. Proses yang terjadi di dalam siklus urea



Urea Cycle Overview Amino acids come from recycling (glutamine), muscle glycolysis (alanine), and diet.



Begin in the Mitochondrion



Summary of Amino Acid Catabolism KATABOLISME KERANGKA KARBON ASAM AMINO Kerangka C asam amino amfibolik ( senyawa keto)



senyawa



Asam amino yg membentuk senyawa amfibolik anggota siklus asam sitrat : Oksaloasetat, fumarat, suksinil KoA, ketoglutaratbersifat glukogenik (dapat membentuk glukosa) Asam amino yg membentuk piruvat akan membentuk oksaloasetat bersifat glukogenik Asam amino yg membentuk asetil KoA (tidak lewat piruvat) / aseto asetil KoA bersifat ketogenik, dapat membentuk senyawa keton



PRODUK KHUSUS ASAM AMINO



PRODUK KHUSUS



Glisin



heme, purin, glutathion, kreatin, asam glikokholat



Metionin



donor gugusan metil



Arginin



kreatin



Histidin



histamin



Triptofan



serotonin



Fenilalanin, Tirosin



melanin, adrenalin, noradrenalin, tiroksin



Glutamat



GABA (Gamma Amino Butiric Acid)



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