HNF 461 1st Edition Lecture 29 Outline of Last Lecture I Amino Acid Metabolism Generally II Liver III Liver Protein Synthesis IV Liver Nitrogen Containing Compound Synthesis a Gluathione b Carnitine c Creatine d Carnosine e Choline V Anabolism of Amino Acids VI Central Dogma Outline of Current Lecture I Amino Acid Catabolism a Transamination b Deamination II Amino Acids and the TCA Cycle III Urea Cycle IV Production of Urea V Urea Cycle and Ammonium VI Amino Acid Metabolism in Various Tissues a Muscle b Kidney c Brain Current Lecture Hepatic Amino Acid Metabolism Pt 2 These 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 1 Amino Acid Catabolism Occurs in the liver except for branched chain amino acids metabolized by muscle bypass the liver when travelling in blood a Transamination i Requires vitamin B6 in the form of PLP ii Enzymes are amino acid specific iii Glutamate usually donates amino group iv Pyruvate Alanine uses ALT enzyme found in muscle and liver v Oxaloacetate Aspartate uses AST enzyme 1 Aspartate required for urea cycle b Deamination i Usually occurs to glutamate 1 Only amino acid that can undergo oxidative deamination ii Releases free ammonia cannot allow free ammonia to build up in the blood body has controls to maintain homeostasis 1 Excretion in urine as ammonia inorganic form 2 Ammonia H ammonium organic form excreted in urine 3 Gut can reverse these processes by producing ammonia from urea 2 Amino Acids and the TCA Cycle a Different amino acids enter the TCA cycle in various places i Glucogenic amino acids contribute to the formation of oxaloacetate to form glucose ii Keteogenic amino acids contribute to the formation of acetoacetate or acetyl CoA cannot contribute to the formation of glucose iii Nitrogen can never enter the TCA cycle 3 Urea Cycle Acts to remove extra nitrogen in the form of ammonia a In mitochondria i Free ammonia NH3 from amino acid deamination combines with a phosphate group and carbon dioxide requires 2ATP Carbamoyl PO4 ii Carbmoyl PO4 combines with ornithine citrulline iii Citrulline leaves mitochondria and travels to cytoplasm b In cytoplasm i Citrulline combines with aspartate arginino succinate requires ATP ii Arinino succinate arginine releases fumarate which travels to TCA cycle iii Urea produced from conversion of arginine ornithine 4 Production of Urea a Higher protein diets produce more urea than lower protein diets 16 g day produced b Urea is main form of nitrogen in the urine c 75 of urea produced goes to urine d 25 of urea produced goes to intestine i Metabolized by intestinal bacterial and converted back to ammonia e Concentration of urea in the blood BUN travels in blood from liver to kidney 5 Urea Cycle and Ammonium a Urea cycle enzymes adapt to protein content of diet i Amount of enzymes in urea cycle depends on the intake of protein protein deficiency low concentration of enzymes ii Liver disease patients are put on a low protein diet to minimize nitrogen concentrations also acidify the colon to increase conversion of ammonia to ammonium then excreted in the feces 6 Amino Acid Metabolism in Various Tissues a Muscle i Branch Chain Amino Acids Leucine Isoleucine and Valine 1 Converted to free ammonia glutamate glutamine carries nitrogen out of cells ii Releases alanine and glutamine iii Releases creatinine iv Releases 3 methylhistidine b Kidney i Glutamine enters kidney is converted to ammonia combines with hydrogen ions to from ammonium and is excreted via urine ii Gluconeogenesis c Brain i Formation of neurotransmitters from amino acid precursors
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