PRACTICAL B: Transamination and deamination Flashcards
Why is deamination important?
So that the carbon skeleton of excess amino acids can be used as a metabolic fuel, or in the synthesis of other compounds for E storage
What is the aim of transamination and deamination?
Channeling the amino nitrogen of amino acids into urea for excretion.
Which enzymes move amino groups between aa and oxoa?
Transaminases (amino transferases)
Which enzyme catalyses the oxidative deamination of glutamate?
Glutamate dehydrogenase
Why are amino groups channeled to glutamate?
E can undergo oxidative deamination, which releases an ammonium ion
Why is aspartate important?
Amino groups can be channeled to aspartate which may contribute its amino group directly in the synthesis of urea.
In the experiment, how were the transamination and deamination reactions followed?
By means of TLC
What is the stationary phase in TLC?
A thin layer of very fine particles. Usually silica gel, has free Si-O-H groups which can H bond.
May also be: aluminium oxide or cellulose, etc.
How is separation effected in TLC?
By allowing a solvent mixture to flow up the surface by capillary action, analytes have different interactions with the matrix and thus will adsorb at different distances from the starting point.
What do transaminases do?
aa1 + oxoa1 —> aa2 + oxoa2
They transfer an amino group from an amino acid to an oxoa to give a different aa and oxoa.
e.g pyruvate + glutamate —-> alanine + 2-oxoglutarate
What’s the cofactor of transaminases?
Pyridoxal phosphate: forms a Schiff’s base with a Lys residue, then with the aa.
What is the value of Keq for transaminases?
Close to 1: reactions are freely reversible which allows for rapid interconversion on aa and oxoa to funnel amino groups to aspartate (used in the urea cycle) or to glutamate (which can then undergo oxidative deamination.
How is the amino group removed from glutamate?
By oxidative deamination, catalysed by glutamate dehydrogenase:
Glu + H2O —–> 2-oxoglutarare + NH4+
What is the cofactor of E dehydrogenase?
NAD+ or NADP+ (v unusual)
After oxidative deamination, what happens to the ammonium ion?
It is transported to the liver as glutamine, where it is converted to carbamoyl phosphate which feeds directly into the urea cycle!
What does the combination of transamination and deamination result in?
The removal of amino groups from aa, which allows oxidation of the carbon skeletons while the amino groups are excreted as urea.
Why was the heart extract dialysed exhaustively?
To remove free amino acids which would have lead to inconclusive results in the TLC analysis.
Outline the experimental procedure (4 steps)
- Make up incubation mixtures (aa, oxoa, cofactors) and add the heart extract last, after that incubate the tubes for 30min at 37ºC
- Stop the reaction by adding ethanol (tubes 1-4) and 2,4-dinitrophenolhydrazine solution (tubes 5-10)
- Place tubes 5-10 back in the 37ºC water bath for 5 minutes and add ethyl acetate, to extract the diphenylhydrazones. Centrifuge all ten tubes.
- TLC
Why is 2,4-dinitrophenylhydrazine used?
DNPH was used to label the oxo acids yellow and produce a hydrazone by reaction with the free keto group.
It detects the C=O functional group and forms a precipitate (dinitrophenylhydrazones) which is yellow in colour
Why is ninhydrin used?
Ninhydrin reacts with the amino group of the free amino acid which upon further decarboxylation and removal of an aldehyde produces an adduct which forms a purple complex with another molecule of ninhydrin.
What are the reactions in tubes 3,4,7 and 8?
3,7: Pyr + Glu —–> Ala + 2-OG
4,8. Glu + NAD —–> 2-OG + NH4+
What is the solvent system for the amino acids?
Ethanol : aqueous ammonia (70:30)
What is the solvent system for the oxoacids?
N-butanol : ethanol : aqueous ammonia (70:10:20)
