Protein Metabolism II - Protein Metabolism 2 Reading:...

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Protein Metabolism 2 Reading: Gropper 4 th ed, Ch 7, pp. 188–194, 207–218 Gropper 5 th ed, Ch 6, pp. 198–206, 222–234
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2 Objectives for today: Amino acid catabolism revisited Genetic disorders of protein metabolism Protein quality Synthesis of proteins and other selected nitrogen-containing compounds
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3 Skeletal Muscle and Protein Metabolism 40% of body’s protein is in muscle 43% of mass is skeletal muscle Uptake of amino acids high following meal 6 amino acids catabolized greatest here: Aspartate, asparagine, glutamate, leucine, isoleucine and valine
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4 Table 6-1a, p. 186 Branched-chain amino acids Branched-chain amino acids
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5 Skeletal Muscle and Protein Metabolism Expression of BC aminotransferases required Muscle, heart, kidney, diaphragm, and adipose 2200 α -keto acids generated may be further oxidized or transported for reamination 2200 α -keto acid is decarboxylated by BC α -keto acid dehydrogenase (BCKAD) Complete oxidation of: Valine yields succinyl CoA Isoleucine yields succinyl CoA and acetyl CoA Leucine yields acetyl CoA and acetoacetate
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6 Fig. 7-38b, p. 213 (Small intestinal cell energy source)
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7 Fig. 7-34, p. 209 Alanine-glucose cycle (Leu, Ile, Val)
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8 Human genetic disorders in amino acid metabolism Name Enzymes/factors affected Amino acid affected Clinical/ symptom PKU Phe hydroxylase Phe Tyr Mental retardation Maple syrup urine disease (MSUD) Branched-chain α - ketoacid dehydrogenase; α -Keto acid decarboxylase Branched- chain amino acid breakdown Mental retardation Fatal Homo- cystinuria Cystathionine synthase Met breakdown, Cys synthesis Increase urinary homocysteine & Met .
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9 Phenylketonuria (PKU) Most common enzyme deficiency disease in amino acid metabolism (1 in 14,000) Autosomal recessive inheritance; many different mutations in phenylalanine hydroxylase identified Phenylalanine accumulates in all fluids; normally “minor” products are formed in excess and excreted in urine (and sweat) Phenylketones: Phenylpyruvic acid (formed by transamination) Phenylacetate (oxidation product of phenylpyruvic acid with “mousey” odor)
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10 Phenylketonuria (PKU) Can cause severe neurological symptoms and very low I.Q. Due to competition for transport of other large, neutral amino acids (L transporter) across blood-brain barrier in the brain Patients often have decreased melanin, resulting in light-colored skin, eyes, and hair Suggests tyrosine deficiency Tyrosine is a precursor of several neurotransmitters and thyroid hormones, as well as melanin Dietary sources of tyrosine are not sufficient
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11 Child with phenylketonuria – inappropriate diet resulted in delayed development
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12 Fig. 6-28, p. 213 PKU (Neurotransmitters) (glucogenic) (ketogenic)
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13 Phenylketonuria (PKU) Treatment: life-long adherence to low-phenylalanine, tyrosine- sufficient diet Some phenylalanine is necessary for growth PKU diet: Eliminate or limit high-protein foods
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Protein Metabolism II - Protein Metabolism 2 Reading:...

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