NUTR 470 1st Edition Lecture 21 -Metabolism of Amino Acids• All tissues have some capability for synthesis of the non-essential amino acids, amino acid remodeling, and other derivatives that contain nitrogen.• However, the liver is the major site of nitrogen metabolism in the body. -Catabolism of Amino Acids • Removal of a-amino group is a two step process.• Transamination reaction-Transamination typically initiates amino acid catabolism.• Oxidative deamination-Removal of the amine from glutamate produces an ammonium ion. -Catabolism of Amino Acids• Transamination reaction-Transamination is the reaction between an amino acid and an alpha-keto acid.-Once the keto acids have been formed from the appropriate amino acids by transamination, they may be used for several purposes.• Fate of keto-acids -The keto acids formed by transamination can be oxidized completely into carbon dioxide and water by the citric acid cycle.-When proteins are in excess, amino acids are converted into pyruvate and acetyl-CoA, and then into lipids by the lipogenesis process.• Generation of keto-acids-If carbohydrates are lacking in the diet or if glucose cannot get into the cells (as indiabetes), amino acids are converted into pyruvate and oxaloacetate, and then into glucose.-Amphibolic intermeidates formed from carbon skeletons of amino acids-The Fate of Amino Acids-Six amino acids form pyruvateThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-When proteins are in excess• Forming pyruvate-All of the carbons of glycine, serine, alanine, systein, and two carbons of threonine form pyruvate and subsequently acetyl-CoA.• Ala Cys, Gly Hyp, Ser Thr —> Pyruvate —> Acetyl-CoA-Six amino acids are forming pyruvate, which enters tricarboxylic acid cycle for complete oxidation to generate energy.-Acetyl-CoA generated by the oxidation of pyruvate can be converted into lipid through lipogenesis. -Six amino acids are forming pyruvate, which is then converted into oxaloacetate by pyruvate carboxylase, and then phosphoenolpyruvate by phosphoenolpyruvatecarboxykinase.-Glucogenic amino acids are used to produce glucose under fasting or starvation conditions. -Catabolism of Amino Acids-Twelve amino acids form acetyl-CoA• Forming acetyl-CoA-Six amino acids form pyruvate and subsequently acetyl-CoA.• Leu Lys, Phe Trp, Tyr —> Acetoacetyl-CoA —>Acetyl-CoA• Ile, Leu, Trp —> Acetyl-CoA-The Fate of Amino Acids-When proteins are in excess• Forming acetyl-CoA-Acetyl-CoA generated by the oxidation of pyruvate is converted into lipid through lipogenesis. -The Fate of Amino Acids-When glucose is not enough• Forming acetyl-CoA-In the liver, acetyl-CoA is converted to ketone bodies, which are used as a fuel byextrahepatic tissues.-The Fate of Amino Acids• Glucogenic amino acids-A glucogenic amino acid is an amino acid that can be converted into glucose through gluconeogenesis.-Hormonal Regulation of Glucose Production from Amino Acids• Favoring gluconeogensis-Cortisone and cortisol from the adrenal cortex stimulate the synthesis of glucose from amino acids in the liver and also function as antagonists to insulin.-The Fate of Amino Acids• Ketogenic amino acids-A ketogenic amino acid is an amino acid that can be converted into ketone bodies.• threonine, isoleucine, phenylalanine, tyrosine and tryptophan• leucine and lysine-The Fate of Amino Acids• Other role of amino acids-Tryptophan is a precursor of the neurotransmitter serotonin-Glycine is a precursor of porphyrins such as heme.-Arginine is a precursor of nitric oxide.-Glutamate and ornithine form neurotransmitter g-amnobutyrate.-Tyrosine forms epinephrine and norepinephrine. -Metabolism of Proteins and Amino Acids• Biosynthesis of non-essential amino acids• Human can synthesize 12 of the 20 common amino acids from the amphibolic intermediates of glycolysis and of the TCA cycle.-Metabolism of Proteins and Amino Acids • Biosynthesis of non-essential amino acids• The combined effect of those three enzymes is to transform ammonium ion into the a-amino nitrogen of various amino acids.• Glutamate dehydrogenase, glutamine synthase, and aminotransferase occupy central positions in amino acid biosynthesis.-Summary• Overview of catabolism of amino acids• Glucogenic/ketogenic amion acids• Fate of amino acids• Biosynthesis of non essential• amino