Transcript Slide 1
Amino Acid Metabolism Intestinal Epithelia: synthesize apoproteins (for lipoproteins) synthesize digestive enzymes glutamine degradation is a primary source of energy and ammonia synthesize alanine, proline, & citrulline (urea formation)… Liver: 50% - 65% uptake from portal blood ~50% hepatic NRG from non-bcaa ~ 20% for synthesis of enzymes & various serum proteins albumin, globulins, acute phase proteins, heat shock proteins blood clot proteins, and others… carnitine, glutathione, creatine, carnosine, choline, pyrimidines, purines… ~ 20% for synthesis of: glucose ketone bodies cholesterol fatty acids More amino acid metabolism… Nerves / CNS: synthesis of: melatonin, serotonin, norepinephrine, dopamine, GABA, ACTH, somatotropin, glycine & taurine can be inhibitory, aspartate & glutamate can be exitatory… Muscles: branched-chain AA catabolism, alanine & glutamine synthesis Kidney: creatine, glucose, ammonia (to reduce serum) pH… Antioxidant HCl release, local immune responses A few examples of the anabolic fate of some amino acids… Hormone / Antioxidant Electron carrier Components of DNA and RNA molecules Substrate for a variety of antioxidant functions Neurotransmitter Creatine-Phosphate is a high-energy compound useful for hard exercise Carnitine is necessary for FA transfer across cell membranes Neurotransmitter / neurotransmitter / hormone Glutamine & glutamate are central to whole body amino acid catabolism. Ammonia released from aa oxidation is transported to the liver in the form of glutamine for urea synthesis. Alanine production from the muscles serves as the main gluconeogenic precursor for both liver and kidney. The carbon skeletons from amino acids enter the TCA cycle at various points… While most amino acid catabolism occurs in the liver, the amino acids marked with * are predominantly catabolized in nonhepatic tissues: skeletal muscle, heart, kidney, adipose tissue… Structures of the bcaa’s have been illustrated… Note that several amino acids can be directly (or indirectly) converted into Acetyl CoA Ammonia released from aa oxidation is transported to the liver in the form of glutamine for urea synthesis. Glutamine is deaminated to glutamate and the free amino group enters the urea cycle for synthesis of urea. Aspartate is synthesized from glutamate and oxaloacetate by glutamate-oxaloacetate transaminase and the resulting aspartate also is necessary for the urea cycle . . . Urea is then excreted by the kidneys . . . Note the relationships between the different amino acids and the TCA cycle and urea cycle… Alanine-Glucose cycle is important for transporting nitrogen to the liver from muscles and in gluconeogenesis, DNA synthesis ... Its major function is to remove “excess” pyruvate from the muscles in the form of alanine and convert the alanine into glucose in the liver for transport back to the muscles – in effect, “recycling” the excess pyruvate into glucose . . . Not a bad idea, especially during high-intensity exercise when rates of glycolysis exceed those of TCA and ETC; obviously this will reduce the buildup of lactate in the muscle cells, reducing osmotic pressure because alanine readily diffuses out of muscle cells while lactate does not. . .