Nutritional biochemistry-Amino Acid Metabolism

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Amino Acid Metabolism

營養生化學(0070210)

Nutritional biochemistry

保健營養學系三年級

授課教師：保健營養學系趙振瑞(Jane Chao)教授

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Learning Objectives

• Amino acid classification (0.5 h)

• Amino acid digestion and absorption (0.5 h) • Amino acid metabolism (1.5 h)

• Interorgan flow of amino acids and

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References

• Gropper SS, Smith JL, Groff JL. Advanced Nutrition and

Human Metabolism, 5th ed. Wadsworth: Belmont, 2009.

• Gropper SS, Smith JL, Groff JL. Advanced Nutrition and

Human Metabolism, 4th ed. Wadsworth: Belmont, 2005.

• Groff JL, Gropper, SS. Advanced Nutrition and Human

Metabolism, 3rd ed. Wadsworth Thompson Learning: Belmont, 2000.

• Linder MC. Nutritional Biochemistry and Metabolism: with

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Essential (indispensable) amino acids (

EAAs

)

• BCAAs: leucine, isoleucine, valine

(branched-chain amino acids; BCAAs)

• basic AAs: lysine

(totally indispensable),

arginine

(conditional),

histidine

(infant)

• aromatic AAs: tryptophan, phenylalnine

• hydroxylic AA: threonine

(totally indispensable)

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Amino acid absorption

• Brush border

membrane absorption

Na

+

-dependent active transport

Na

+

-independent active transport

Enterocyte Lumen (small intestine) Amino acids Amino acids Brush border membrane Carrier Gropper et al. 2005

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10 Step 1 Amino acid transporter Cytosol Intracellular amino acid metabolism Na+_/K+ ATPase Step 2 Cell membrane Step 3 Step 4 Step 5 Amino acid Amino acid Amino acid Amino acid Amino acid Na+ Na+ Na+ Na+ Na+ Na+ Gropper et al. 2005

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12 Na1 Na1 Na1 Na1 Na1 Na1 K1 _K1 Required for some amino acid transport Amino Acid Enterocyte Lumen Amino Acids Basolateral Membrane Carrier Brush border membrane Amino acids ADP 1 ATP P_i Peptides Na+_/K+_-ATPase Gropper et al. 2005

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Amino acid absorption

• most rapidly absorbed AAs

• branched-chain AAs > smaller AAs

• neutral AAs > dibasic or dicarboxylic AAs

• EAAs > NEAAs

• Met, Leu, Ile, Val

• Most slowly absorbed AAs

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• 何種胺基酸在人體小腸吸收較快？

(1) Glycine (2) Methionine (3) Tyrosine (4) Arginine http://www.mfi.ku.dk/ppaulev/chapter22/kap%2022.htm

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Transaminase

(

₍

aminotransferase

_{aminotransferase}

)

₎

• alanine aminotransferase (ALT)

glutamate pyruvate transaminase (GPT)

higher concentrations in liver, heart, kidney

• aspartate aminotransferase (AST)

glutamate oxaloacetate transaminase (GOT) higher concentrations in heart, liver, muscles

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= GPT

= GOT

Gropper et al. 2005

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22 alanine cycle deamination ureagenesis transamination Gropper et al. 2005

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23 2C 6C 4C 4C CO₂ mitochondria N-acetylglutamate mitochondria cytosol H₂N-C- NH₂ O Gropper et al. 2005

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• 何者不是人體代謝胺基酸的生化反應？

(1) Cori cycle (2) Deamination (3) Glucose-alanine cycle (4) Urea cycle http://www.mmi.mcgill.ca/mmimediasampler2002/

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Glutamine utilization in intestine

glutamine glutamate α-ketoglutarate TCA cycle ATP production glutaminase NH₄+ (ammonium) glutamate dehydrogenase NH₄+ NADP+ _(NAD+₎ NADPH (NADH) + H+ glutamine glutamate α-ketoglutarate TCA cycle ATP production glutaminase NH₄+ (ammonium) GPT (ALT) pyruvate alanine deamination transamination

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Ketogenic: Leu, Lys

Partially ketogenic and glucogenic Glucogenic

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Amino acid metabolism in skeletal muscles

• synthesized de novo and released into the blood alanine (ala), glutamine (gln)

• catabolized in skeletal muscles for utilization

aspartate (asp), asparagine (asn), glutamate (glu), leucine (leu), isoleucine (ile), valine (val)

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Amino acid metabolism in kidney

• synthesized de novo and released into the blood arginine (arg), histidine (his), serine (ser)

• catabolized in kidney for utilization

aspartate (asp), glutamine (gln), phenylalanine, alanine (ala), glycine, citrulline (cit)

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Amino acid metabolism in brain

• synthesized de novo and released into the blood

glutamine (gln)

• catabolized in brain for utilization

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alanine cycle

anaerobic glycolysis

Cori cycle

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1-1.8 g N/d

0.3-1.0 g N/d

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Summary

• The amino acids comprising the pools are used in a

variety of ways.

• The liver is the primary site of amino acid

metabolism. Of particular significance is the metabolism of branched-chain amino acids in skeletal muscles and the production of the

ammonium ion in the kidney.

• Glutamate, glutamine, and alanine play the

important roles in various metabolic pathways for amino acids.