32 AAs - Fates

32 AAs - Fates - Amino Acids and Proteins Metabolism Amino...

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Unformatted text preview: Amino Acids and Proteins: Metabolism: Amino Acid Fates HNFE 3025 Fall 2009 Catabolism of AAs Fig. 6-34, p. 221 2 • 1st step is the removal of the α-amino group resulting in an α-keto acid (carbon skeleton) – Transamination – transfer of amino group from one AA to another AA – Deamination – remove the amino group with no direct transfer to another compound AA Catabolism 3 The fate of the AA C-skeleton depends on the AA from which it was derived and the nutritional state of the body • Catabolized immediately for energy • GNG Glucose which is subsequently catabolized for energy • Ketone bodies – possible because acetoacetate and acetyl CoA are products for some AAs • Fatty acids – technically feasible by de novo FA synthesis using acetyl CoA from AAs (normally insignificant) • Cholesterol – potential fate since acetoacetate and acetyl CoA generated Fates of the α-keto acid (carbon skeleton) 4 • All or part of the carbon skeleton (18 AAs) can be converted into glucose – The carbon skeletons are degraded to pyruvate, or a 4-C or 5-C TCA cycle intermediate • When glucose levels are LOW, these are the major carbon sources for GNG – The carbon skeletons can also be immediately catabolized for energy without being converted to glucose. – Utilizing AAs to replenish the TCA cycle intermediates that are used for other metabolic processes is known as anaplerosis. Glucogenic AAs 5 • Carbon skeletons of leucine and lysine are degraded to acetyl CoA (or acetoacetate) – Because acetyl CoA cannot be converted to glucose, it is • Catabolized for energy in TCA cycle • Converted to ketone bodies • (Potentially) converted to fatty acids Ketogenic AAs 6 • 5 AAs (Ile, Trp, Phe, Tyr, Thr) can be described as both ketogenic and glucogenic – Part of their carbon skeletons are degraded to acetoacetate (Phe, Trp, Tyr) or acetyl CoA (Ile, Thr) – Part of their carbon skeletons become pyruvate (Thr, Trp), succinyl CoA (Ile) or fumarate (Phe, Tyr) Some AAs are Both Glucogenic and Ketogenic 7 Fates of AA Carbon Skeletons 8 Acetyl-CoA TCA Cycle Acetoacetate Pyruvate Oxaloacetate Fumarate Succinyl-CoA α-Ketoglutarate Citrate Isocitrate Malate LEUCINE LYSINE Phenylalanine Tryptophan Tyrosine Alanine Cysteine Glycine Serine Threonine Tryptophan LEUCINE Isoleucine Threonine Asparagine Aspartate Phenylalanine Tyrosine Arginine Glutamine Glutamate Histidine Proline Isoleucine Methionine Valine = Glucogenic = Ketogenic Catabolism of Phe and Tyr 9 • Phe – Supplies approximately...
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This note was uploaded on 03/23/2010 for the course HNFE 3025 taught by Professor Mwhulver during the Spring '10 term at Virginia Tech.

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32 AAs - Fates - Amino Acids and Proteins Metabolism Amino...

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