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Chapter 26 Amino Acids Metabolism
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26.1 Biosynthesis of Amino Acids
Essential Amino Acids Ile Leu Lys Met Phe Thr Trp Val The amino acids can be grouped together into six biosynthetic pathways depending on the intermediate from which they are derived.
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TCA CYCLE a-Ketoglutarate Oxaloacetate Glu Asp Gln Pro Arg Asn Met Thr Lys a-Ketoglutarate Ile family ( Glutamate family) Aspartate family
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GLYCOLYSIS 3-Phosphoglycerate Pyruvate Ser Ala Val Leu Cys Gly Pyruvate family 3-Phosphoglycerate family ( Serine family)
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PENTOSE PHOSPHATE GLYCOLYSIS PATHWAY Phosphoenolpyruvate Erythrose 4-phosphate Ribose 5-phosphate Phe Tyr Trp His Phosphoenolpyruvate and Histidine Erythrose 4-phosphate family ( Aromatic family)
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26.2 Amino Acid Degradation
The amino acids are degraded by 20 different pathways that converge to just 7 metabolic intermediates Pyruvate a-Ketoglutarate Succinyl-CoA Fumarate Oxaloacetate Acetyl-CoA Acetoacetate
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Glucogenic Ketogenic
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deamination
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transamination
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26.2.4 decarboxylation decarboxylase RCHNH2COOH RCH2NH2 + CO2
a-Amino Acid amine Pyridoxyl Phosphate
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26.3 Ammonia Excretion Glucose-alanine cycle IN MUSCLE
NH4+ + a-Ketoglutarate + NADPH + H+ glutamate dehydrogenase Glu + NADP+ + H2O alanine transaminase Glu + Pyruvate a-Ketoglutarate + Ala IN LIVER Ala + a-Ketoglutarate Pyruvate + Glu
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The excess nitrogen is first converted into ammonia and is the excreted from living organisms in one of three ways. Many aquatic animals simply excrete the ammonia itself directly into the surrounding water. Birds and terrestrial reptiles excrete the ammonia in the form of uric acid, while most terrestrial vertebrates convert the ammonia into urea before excretion. These three classes of organisms are called: ammonotelic, uricotelic and ureotelic, respectively.
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26.4 The Urea Cycle Carbamoyl phosphate synthetase
Ornithine transcarbamoylase Argininosuccinate synthetase Argininosuccinase Arginase
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The overall reaction of the urea cycle
NH4+ + HCO3- + H2O + 3ATP + aspartate urea + 2ADP + AMP + 2Pi + PPi + fumarate
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