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

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Amino Acids and Proteins: Metabolism: Amino Acid Fates HNFE 3025 Fall 2009
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Catabolism of AAs Fig. 6-34, p. 221 2
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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
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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
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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
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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
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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
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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
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Catabolism of Phe and Tyr 9 Phe Supplies approximately 50% of Tyr needs Can be metabolized and
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