1Chapt. 39Ch. 39Student Learning Outcomes:• Explain basic synthesis of nonessential amino acids• Uses glucose derivatives (glycolysis, TCA)• N sources often other aa• Describe important cofactors:• PLP (from Vitamin B6) for transaminations• FH4(tetrahydrofolate) for 1C; • BH4(tetrahydrobiopterin) for hydroxylation • (Phe → Tyr)• Explain general regulation of amino acid synthesis (feedback inhibition, transcription inhibition)• Degradation of aa often distinct from synthesis pathOverview synthesis of nonessential amino acidsFig. 39.1*Overview synthesis of nonessential amino acids:• Met donates the S to Cys• C skeletons come from glucose, glycolysis, TCA compounds• Aa that can be synthesized are often used for other N cmpds:• Gly → purine, pyrimidine• Asp → purine, pyrimidine• Gln → neurotransmitterOverview Degradation of amino acidsFig. 2Overview: degradation of amino acids:A. Gluconeogenic: Pyruvate, TCA intermediatesB. Ketogenic: Acetyl CoA, ketone bodiesSome genetic disorders of amino acid metabolismDegradationpath enzyme disease symptomsPhe phe hydroxylase (PAH) PKU classic mental retardationhomogentisate oxidase alcaptonuria black urine, arthritisTyr fumarylacetoacetate hydrolase tyrosinemia I liver failure, deathtyrosine aminotransferase tyrosinemia II neurologicalMet cystathionase cystathionuria benigncystathionine b-synthase homocystinemia cardiovascular,neurologicalGly glycine transaminase oxaluria type 1 renal failure(Gly → oxalate) Ca-oxalate stones2Metabolism of Phe/TyrFig. 39.15Phe and Tyr:• PKU from absence PAH (autosomal recessive); 1/104births; all babies tested;give special diet of low Phe (essential aa)High Phe in blood → neurological• Tyr is made from Phevarious defects in degradationneurological, liver failureCysteine metabolismFigs. 39.6 CysCysteine metabolism:• C, N from Ser, S from Met• Met donates S to Cys via Homocys• Removal of –CH3• Cystathionine precursor of Cys• Feedback regulation of synthase• Adjust for dietary Cys• Lack of synthase →
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