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16 Cards in this Set

  • Front
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Various aspects of amino acids

-Position of -NH2 α-AA (in proteins), b-AA (b-alanine), γ-AA (GABA) ... etc.


-Configuration on C* L-amino acids (most) ´ D-amino acids (? unknown function)


-Acide-base properties „amino-acidic“ (15) ´ acidic (2) ´ basic (3)


-Side chain character non-polar (9) ´ polar (6) ´ ionized (5)


-Availability for humans essential (9) ´ semiessential (3) ´ non-essential (11)


-Metabolism glucogenic (13) ´ ketogenic (2) ´ mixed (5)


-Occurence in proteins proteinogenic (20) ´ non-proteinogenic (e.g. ornithine, homocysteine)

Three sources of AA pool:

1)Proteolysis of dietary proteins(food)


2)Proteolysis of tissue proteins (physiological turnover,more in starvation)


3)Synthesis of non-essential AA(11)

Three utilizations of AA pool:

1)Synthesis of tissue and bloodplasmaproteins (liver)


2)Synthesis of low-molecular nitrogen compounds (with specific functions)


3)Catabolism: deamination + utilization of carbonskeleton

Three utilizations of AA carbon skeleton

1)Gluconeogenesis(in starvation,most AA are glucogenic)


2)Synthesis of FAand TAG (inAA excess)


3)Metabolic fuel = gain of energy(minor utilization)

Transcellular transport of AA from intestine to portal blood

Various aspects of amino acids

Endogenous proteins have different biological half-lives >

Degradation of proteins in lysosomes

•doesnot require ATP, non-specific•extracellularand membraneproteins•long-livedintracellular proteins •extracellularglycoproteins – sialic acid at terminal position on oligosaccharide chain isremoved = asialoglycoproteins – they are recognized by liver receptors --> degradationin liver lysosomes

Proteins in nutrition

•daily intake of proteins for adult 0.8 g/kg•four main sources: meat, eggs, dairy products, beans•intake ofanimal and plant proteins should be balanced•animalproteins contain moresulfur AA –more acidifying•proteinquality depends on content of essencial AA, theirratio, and protein digestibility•generally:animal proteins have higher quality thanplant proteins•wheat –deficitof Lys,Trp, Thr, Met•beans –deficitof Met, CyslP

Transamination

•mostAA (not Lys, Thr, Pro, His, Trp, Arg, Met)


•aminogroup is transferred from AA to 2-oxoglutarate


•cofactor– pyridoxal phosphate (® Schiff bases)


•reversible reaction Þimportant for synthesis of AA

Glutamate dehydrogenase (GMD, GD, GDH)

•requirespyridine cofactorNAD(P)+


•GMDreaction is reversible


•dehydrogenation ofCH-NH2 to imino group C=NH


•hydrolysisof imino group to oxo group and ammonia


•allosteric regulation: GTP,ATP, NADH inhibit, ADP activates,


•low energy level incell is the signal for production of 2-oxoglutarate and its oxidation

Two main sources of ammonia in organism

1.Deamination of glutamate (GD reaction) in tissues,mainly inliver and kidneys


2.Bacterial putrefaction of proteins in the large intestine produces nitrogen catabolites(e.g. amines + ammonia), ammoniadiffuses freely into portal blood Þ portalblood has high concentration of NH4+ Þ eliminated by liver

Production of ammonia in the body -overview

Compare: Ammonium ions in body fluids

Acide-base properties of NH3

pKB (NH3) = 4.75 (weak base)


NH3 + H2O ⇄ NH4+ + OH-


pKA (NH4+) = 14 – 4.75 = 9.25 (very weak acid)




under physiological pH values inICF and ECF (~ 7.40):


98% NH4+


2 % NH3

Threeways of ammonia detoxification