Nitrogen metabolism, urea cycle, special AA function -Brar Flashcards
What is the function of glutamate dehydrogenase and where is it found?
in the liver and kidney.
it liberates free ammonia (to enter the urea cycle) from glutamate to form alpha-ketoglutarate (to enter other metabolic pathways)
What is the function of glutamine synthetase?
it converts glutamate into glutamine by the addition of NH3
*uses ATP
glutamine can be transported from the liver to other tissues in the blood
is most active in the liver
What is nitrogen balance?
Nitrogen balance: N consumed - N excreted
because there is no storage of nitrogen
Balance Zero for healthy adults Positive -Childhood -Pregnancy -Muscle building -Healing Negative -Protein malnutrition -Deficiency of essential amino acids -Stress (fever, surgery etc…)
Where do amino groups for urea synthesis enter the urea cycle?
as ammonia (oxidative phosphorylation and transamination to glutamate–> aspartate)
or aspartate directly
How many ATP are used in the urea cycle and at what steps?
2 ATP are used in the formation of carbamoyl phosphate (in the mitochondria matrix)
NH3+ CO2–> carbamoyl phosphate
a 3rd ATP is used in the conversion of aspartate–> arginosuccinate (via arginosuccinate synthase)
Synthesis of catecholamines
tyrosine—> DOPA (via tyrosine hydroxylase, requires tetrabiopterin)
DOPA–> dopamine (via DOPA decarboxylase
Dopamine +ascorbate + O2–> norepinephrine (via dopamine beta hydroxylase)
norepinephrine–> epinephrine (requires SAM) (via phenylethanolamine N methyl transferase)
How is histamine synthesized and what is it’s function?
histidine–> histamine (via decarboxylase)
Involved Allergic response Inflammatory reactions Gastric acid secretion Neurotransmitter Powerful vasodilator Released by mast cells Formation also requires PLP (pyridoxal phosphate)
How is serotonin synthesized? Where is it found?
tryptophan—> 5-hydroxy tryptophan (*requires tetrahydrobiopterin) (via hydroxylase)
5 hydroxy tryptophan–> serotonin (via decarboxylase)
Largest amount found in intestinal mucosal cells
Also in brain
Platelets
Multiple complex roles
How is creatine synthesized and what is its function?
arginine +glycine–> guanidinoacetate (via amidinotransferase)
guanidinoacetate–> creatine (via methyltransferase) (*uses SAM)
creatine –> creatine phosphate (uses ATP via creatine kinase
High energy compound
Small but rapidly mobilized reserve of high energy phosphates
Helps maintain intracellular levels of ATP
How is glutathion synthesized and what is its function?
is a tripeptide of glycine + cysteine + glutamate held by a sulfide bond
Contains unusual linkage between glutamate side chain carboxylate group and the nitrogen of cysteine
Antioxidant role
Transports amino acids across cell membranes
Glutamyl cycle
glutathione reductase reduced glutathione to 2 G-SH (using NADPH)
while glutathione peroxidase oxidizes it to G-S-S-G (using H2O2)
How is NO synthesized and what is its function?
arginine + NADPH–> citrulline + NO (via NO synthase)
Important in macrophages for creating NO for the generation of free radicals which are bacteriocidal
Stimulates the influx of calcium ions into vascular endothelial cells with the activation of cGMP
Results in relaxation of vascular smooth muscle
How is GABA produced and what is the required cofactor?
Inhibitory neurotransmitter
Produced by decarboxylation of amino acids in reactions that use pyridoxal phosphate as cofactor
Produced by decarboxylation of glutamate
How can NAD and NADP be produced? What is the primary precursor of these?
Nicotinamide moiety of NAD and NADP formed from tryptophan
However, the major precursor of nicotinamide is the vitamin niacin
What AA are thyroid hormones produced from?
Follicular cells of thyroid gland produce thyroglobulin
Iodination of tyrosine residues in thyroglobulin produces
Monoiodotyrosine (MIT)
Diiodotyrosine (DIT)
MIT and DIT undergo coupling reactions to produce
3,5,3’-triiodothyronine (T3)
3,5,3’,5’-tetraiodothyronine (T4)
Also known as thyroxine
