Amino_Acid_Catabolism_Lecture

Provide an example of how amino acid

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Unformatted text preview: nd beta- hydroxybutyrate are collec-vely called ketone bodies. Synthesis of ketone bodies will be discussed in detail in lipid oxida-on. The point of this slide is to provide an example of how amino acid breakdown leads to citric acid cycle intermediates and ketone body precursors. There is no need to know the individual steps. Hopefully by this -me you will have an apprecia-on for why citric acid cycle sits in the center of metabolic pathways. Citric acid cycle reac-ons can be considered a collec-on of reac-ons that connect various metabolites important in oxida-on and synthesis of carbohydrates, amino acids, and lipids. In skeletal muscle, keto- acids from amino acid oxida-on enter citric acid cycle or become acetyl- CoA or acetoacetyl- CoA (which is converted to 2 acetyl- CoA by thiolase). The ammonia from amino acid oxida-on is transported from muscle to liver as alanine, which enters gluconeogenesis as pyruvate (keto- acid of alanine) to form glucose. Glucose can be transported back to muscle for glycolysis and product of glycolysis, pyruvate, can be used for alanine synthesis. This glucose- alanine cycle depends upon glutamate and alaine aminotransferase. Alanine aminotransferase (ALT) is a major diagnos-c tool for liver damage like hepa--s. Upon liver damage, ALT is found in blood. Urea cycle takes place in liver cells (hepatocytes), not outside liver. Amino –transferases u-lize pyridoxal phosphate as co- factor. The key to pyridoxal phosphate func-on in transamina-on is forma-on of a Schiff base intermediate. The above mechanism describes half of the amino- transferase reac-on, the other half goes backward with a different keto- acid. This is classic ping- pong mechanism reac-on. Schiff base is also the present in intermediate structures in decarboxyla-on reac-ons. For examples, see Figure 14- 5 (p. 534) and Figure 14- 14 (p. 550)....
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