kuliah metab aa ys 2013(4)

8/13/2019 Kuliah Metab Aa Ys 2013(4)

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OVERVIEW OF AMINO ACID METABOLISM

ENVIRONMENT ORGANISM

Ingestedprotein

Bio-synthesis Protein

AMINOACIDS

Nitrogen Carbon

skeletons

Urea

Degradation(required)

1 2 3

a

b

PurinesPyrimidinesPorphyrins

c c

Used forenergy pyruvate

-ketoglutaratesuccinyl-CoAfumarateoxaloacetate

acetoacetateacetyl CoA

( glucogenic) (ketogenic)


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NITROGEN BALANCE

Nitrogen balance = nitrogen ingested - nitrogen excreted

(primarily as protein) (primarily as urea)

Nitrogen balance = 0 ( nitrogen equilibrium)

protein synthesis = protein degradation

Positive nitrogen balance

protein synthesis > protein degradation

Negative nitrogen balance

protein synthesis < protein degradation


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N bal ance = N i n

- N out


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Pos i t ive Nit ro g en B alan c e


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Metabo l ic Poo l o f A m ino A c ids


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Amino Acid Requirements of Humans--------------------------------------------------------------------Nutritionally Essential Nutritionally Nonessential--------------------------------------------------------------------

Arginine a AlanineHistidine AsparagineIsoleucine AspartateLeucine CysteineLysine GlutamateMethionine GlutaminePhenylalanine GlycineThreonine ProlineTryptophan SerineValine Tyrosine

---------------------------------------------------------------------a Nutritionally semiessential. Synthesized at rates

inadequate to support growth of children.


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Glucose-alanine cycle

Ala is the carrier of ammonia and of thecarbon skeleton of pyruvate from muscle toliver.The ammonia is excreted and the pyruvate isused to produce glucose, which is returned tothe muscle.

Alanine plays a special role intransporting amino groups to liver.

According to D. L. Nelson, M. M. Cox :LEHNINGER. PRINCIPLES OF BIOCHEMISTRY Fifth edition


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The fate of the amino group during amino acid catabolism


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TRANSAMINATION


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Clinicaly important transaminases

ALT

Alanine- a -ketoglutarate transferase ALT (also called g lutamate- p yruvate transaminase GPT )

As partate- a -ketoglutarate transferase AST(also called g lutamate- o xalacetate transferase GOT )

Important in the diagnosis of heart and liver damage caused by heartattack, drug toxicity, or infection.


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FATE OF THE CARBON SKELETONS

Carbon skeletons are used for energy .

Glucogenic : TCA cycle intermediates

or pyruvate (gluconeogensis)

Ketogenic : acetyl CoA, acetoacetyl CoA,

or acetoacetate


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Metabolism of some

selected amino acids


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Histidine Metabolism:Histamine Formation

N

NH

CH 2 CHCO 2-

NH 3+

N

NH

CH 2 CH 2 NH 2

Histidine Histamine

Histidinedecarboxylase

CO 2

Histamine :Synthesized in and released by mast cellsMediator of allergic response: vasodilation,

bronchoconstriction


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Glycine oxidation to CO 2

Glycine produced from serine or from the diet can also be oxidized by glycinedecarboxylase (also referred to as the glycine cleavage complex, GCC) to yield asecond equivalent of N 5,N 10 -methylene-tetrahydrofolate as well as ammonia andCO 2.

Copy from : http://themedicalbiochemistrypage.org/amino-acid-metabolism.html


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A ti


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AromaticAminoAcids

Phenylalanine Tyrosine Tryptophane

fumarate AcetoacetateDopa &

Dopamine Melanine

Norepinephrin

&epinephrine

Thyroxin

Skatol &Indol Melatonin

Anthranilic Serotoninglucose ketone

Alanine Nicotinamide

AcetoacetylCoA


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Hyperphenylalaninemia - complete deficiency of phenylalaninehydroxylase (plasma level of Phe raises from normal 0.5 to 2 mg/dL tomore than 20 mg/dL).The mental retardation is caused by the accumulation ofphenylalanine, which becomes a major donor of amino groups in

aminotransferase activity and depletes neural tissue of -ketoglutarate. Absence of -ketoglutarate in the brain shuts down the TCA cycle andthe associated production of aerobic energy, which is essential tonormal brain development.Newborns are routinelly tested for blood concentration of Phe.The diet with low-phenylalanine diet.

Phenylketonuria


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ALHAMDULILLAH

SEMOGA BERMANFAATYS/2013

kuliah metab aa ys 2013(4)

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