Lec13 aminoac met
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Lec13 aminoac met






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    Lec13 aminoac met Lec13 aminoac met Presentation Transcript

    • Catabolism of the Carbon Skeletons of Amino Acids Twenty amino acid carbon skeletons are funneled into only seven mols. Several enzyme cofactors play important roles in amino acid metabolism. Ten amino acids are degraded to Acetyl-CoA. The dehyrdation of tryptophan is the most complex pathway.
    •  Ketogenic amino acids – aas that are degraded to Acetyl CoA or acetoacetyl CoA • Leu • Lys Glucogenic amino acids – aas that are degraded to pyruvate, -KG, succinyl CoA, fumarate, or OAA – 14 aas Both ketogenic and glucogenic amino acids (PITT) • Phe • Ile • Tyr • Trp
    • Catabolism of the carbon skeletons of amino acidsThe C skeletons of 20 amino acids arefunneled into only 7 molecules: – Pyruvate – Acetyl CoA – Acetoacetyl CoA – -Ketoglutarate – Succinyl CoA – Fumarate – Oxaloacetate
    • Important factors in amino acid metabolism 1-Carbon transfer is a common type of reaction in amino acid metabolism. • CO2 Biotin • 1-C transfer tetrahydrofolate • -CH3 S-Adenosylmethionine
    • Pyruvate is the point of entry for Ala, Ser, Cys, Thr and Trp
    • Catabolicpathway forAsp and Asn
    • Met requires SAM Met is converted to succinyl CoA in 9 steps. S-adenosylmethionine (SAM), formed along this pathway, is an important molecule for transferring methyl groups!
    • Trp as precursor
    • CatabolicPathways forIle, Leu, Val(not in theliver)
    • Branched amino acids are not degraded in liver Leu, Ile,Val are primarily oxidized to their corresponding - ketoacids in extrahepatic tissues like muscle, adipose, kidney, and brain tissue. Branched chain aminotransferase is specific to these tissues.
    • Branched amino acids share the same enzymes for the first 2 reactions Leu Acetyl CoA Ile Acetyl CoA Val Succinyl CoA
    • 2nd enzyme -ketoacid dehydrogenasecomplex may be defectiveThis causes “Maple syrup disease” Mental retardation Infant deaths Burnt maple syrup odor in the body and urine of the patient The levels of -ketoacids and the branched chain amino acids are high!!
    • Screeningtest forMSUD
    • Oxygenases are required for thedegradation of aromatic amino acids Molecular oxygen is used to break an aromatic ring. The degradation of Phe starts with hydroxylation. • Enzyme: Phe hydroxylase – This enzyme is called “monooxygenase (or mixed- function oxygenase) because one atom of O2 appears in the product (tyr) and the other in H2O • The reductant is “tetrahydrobiopterin”(made in the body, not a vitamin)
    • Inborn errors The catabolism of Phe is very important also. Enzyme defects in Phe catabolism lead to several genetic diseases.
    • Diseases related with Phe catabolism Phenylketonuira (PKU) Phenylalanine hydroxylase Alkaptonuria homogentisate 1,2-dioxygenase Tyrosinemia II tyrosine amino transferase Tyrosineamia I -hydroxyphenylpyruvate dioxygenase
    • Degradation ofPhe and Tyr
    • alkaptonuria In 1902, Archibald Garrod described this disease. • Large amounts of homogentisate excreted in the urine. • Zacutus Lusinatus, in 1646, wrote about a patient who passed black urine: “none of the predicted evils ensued, he married, began a large family, and lived a long healthy life, always passing urine as ink!!”
    • PKU Elevated levels of Phe in blood due to the deficiency of “Phe hydroxylase” Autosomal recessive Impaired brain development, mental retardation Treatment: diet low in Phe
    • AlternativePathway for Phedegradation inPKU