Degradation of Amino Acids Flashcards
Protein Digestion, Amino Acids, Tissue Utilization, Degradation of Amino Acids, Fate of Carbon Core, Urea Cycle
BUN in pregnancy
decreased
other sources of alanine besides the muscle
kidney and intestines
CPSI deficiency
Type I hyperammonemia
the second step of urea cycle
citrulline synthesis
Aspartate + citrulline +ATP —> argininosuccinateWhat happes to the nitrogen of aspartate?
gets incorporated into urea
an alternative to low protein diet aimed at reducing the ammonia load on the urea cycle
scavenger drugs
BUN in liver damage
decreased
high levels of N-acetyl glutamate leads to
increased CPSI activity
blood citrulline level in type I and type II
low for both
Glutamate directly provides nitrogen (NH4+) to urea cycle through
deamination by glutamate dehydrogenase
The only place that urea cycle takes place in
liver
The two precursors of argininosuccinate
citrulline and aspartate
the reaction catalyzed by carbamoyl phosphate synthetase I
CO2 + NH4+ – 2ATP —> carbamoyl phosphate
Glutaminase
the enzyme in the kidney that forms NH4+ and glutamate from glutamine
ALT
alanine aminotransferase(Alanine/ a-ketoglutrate) and (pyruvate/ glutamate)
the amino acids that can undergo deamination
glutamate, glycine, serine, threonine, histidine
the product of the step of urea cycle is transported into the cytosol
second step. citrulline gets transported to cytosol
two methods for carbamoyl phosphate synthesis
1- Mitochondria- urea cycle and CPSI2- from glutamine and CO2 by CPSII in cytosol (–> pyrimidine synthesis)
when to provide arginine as urea cycle intermediate
if argininosuccinate lyase is defecient.
ALT level 36hours after ingestion of toxic mushroom
ALT reaches 20X its normal level after 36 hours.Indicates liver cell necrosis- liver as the site for toxic removal
the deficiency of argininosuccinate lyase cased
argininosuccinyl acidemia
the first step in urea synthesis
CO2 + NH4+ – 2ATP —> carbamoyl phosphate
function of glutamate dehydrogenase in other tissues , EXCEPT the liver and kidney
formation of glutamate and water from a-ketoglutarate and NADP+
argininemia is caused by
the deficiency of arginase which catalyzes the cleavage of arginine
main detoxification reaction in brain is catalyzed by this enzymeHint: 1/3 enzymes that fixes free ammonia
glutamine synthetase
the coenzyme of transaminase
PLP- pyridoxal phosphate
deamidation
removal of amide group from glutamine and asparagine as NH4+
BUN and blood ammonia in liver damage
BUN decreased in liver damage But blood ammonia increased during liver damage
importance and the enzyme deamidation of glutamine in kidney
important in kidneyprovides most of the NH4+ in the urineNH3 aids the secretion of protons into the urine and indirectly helps to balance blood PH.Glutaminase is the enzyme
the fate of fumarate as a by product of arginine synthesis (argininosuccinate lyase)
enters the TCA cycle and regenerate oxaloacetate and then aspartate.
carbamoyl phosphate synthesis of urea cycle takes place in
mitochondria
blood nitrogen metabolites
blood urea nitrogen (BUN)creatinine uric acidammonia
The impact of high levels of arginine production on urea production
increased urea production though1- high n-acetyl glutamate –> increased CPSI –> increased urea production2- increased ornithine production –> increased urea production
BUN in kidney damage
increased
how to reduce ammonia load on the urea cycle
low protein diet, avoid fasting - to limit amino acid degradation
Nitrogen is carried to the liver by
alanine and glutamine
activates CPSI
N-acetyl glutamate
The two amino acids that undergo deamidation
glutamine and asparagine
name at least three condition in which plasma ALT And AST are elevated
cirrhosishepatitisliver toxicity
Glutamine —?—> glutamate —?–> a-KGLIVER
GlutaminaseGDH
cleavage of arginine into urea and ornithine is catalyzed by
arginase
the only way arginie is produced in human body
arginine synthesis via argininosuccinate lyase in cytosolArgininosucccinate —> fumarate + arginine
arginase cleaves argininie into
urea and ornithine
conversion of glutamine to alanine
glutamine first to glutamate- E: glutaminaseGlutamate to alanine- E- ALLT
the central role of glutamate in nitrogen removal
transamination - collect nitrogendeamination- provides nitrogen to the urea cycle by glutamate dehydrogenasetransaminating oxaloacetate into asparte- provides nitrogen indirectly to the urea cycle. Aspartate then provides an amino group to ureaprecursor for the allosteric activator of the urea cycle
high levels of arginine leads to
high levels of N-acetyl-glutamateIncreased ornithine production
the energy requirement of argininosuccinate synthesis
1 ATP
the energetics of the urea cycle
aspartate + NH3 + CO2 +3ATP –> Urea + fumarate + 2ATP + 2P + PP + 3H2o
Increased CPSI activity leads to
Increased urea production
energy requirement of carbamoyl phosphate synthesis for urea cycle
2ATP
Increased ornithine production leads to
increased urea production
The allosteric regulator of CPSI
N-acetyl-glutamate
how to limit amino acid degradation
low protein diet and avoid fasting
CPSI or N-acetylglutamate synthase deficiency causes
Type I hyperammonemia
the only X-linked recessive primary hyperammonemias
type II hyperamoonemia- ornithine transcarbamoylase
argininosuccinate synthesis takes place in
cytosol
after citrulline synthesis, it is transported to the
cytosol
Urine orotate for type I a nd type II
type I - lowType II- HighThe only differentiating factors. Other values are identical for the two.
ornithine transcarbamoylase catalyzes the synthesis of ——– in ——.
citrulline in mitochondria
amino acid degradation takes place in all tissues. How does nitrogen gets to the liver?
Nitrogen is carried to the liver by ALANINCE and GLUTAMINE
defeciency in ornithine transcarbamoylase
type II hyperammonemia
aminotransferase
transaminase- an enzyme for the reversible reaction of transamination.
activates the synthesis of N-Acetylglutamate
HIGH levels of arginine
as the utilization of amino acids decreases, urea production ——
decreases
deamination
removal of a-amino group from certain amino acids as NH4+glutamate, glycine, serine, threonine, histidine
net glutamine producers
muscle and brain
PLP
pyridoxal phosphate
The role of glutamate in the following reactionGlutamate + Acetyl-CoA –> N-acetyl Glutamate
1- allosteric activator2- provides nitrogen
blood ammonia in urea cycle disorders
increased
how many high energy phosphate bonds are broken and what does it mean for the urea cycle
4 high energy bonds are broken, which makes the cycle irreversible
how can part of the used energy in urea cycle be recovered?
if fumarate enters the TCA cycleFumarate –> Malate _> Oxaloacertate–> Aspartate and 1 NADH ~ 2.5 ATP through oxidative phosphorylation
CPSI
carbomyl phosphate synthetase I catalyzes the carbamoyl phosphate synthesis- The rate limiting and committed step of urea cycle
three enzymes that can fix free ammonia into organic molecules
glutamate dehydrogenaseglutamine synthetasecarbamoyl phosphate synthetaseI
The reason for decreased level of nitrogen metabolites during pregnancy
increased GFR
Glutamine –?–> glutamate —?–> alanine
glutaminase, ALT
The main pathway of amino acid nitrogen removal is
transamination
Citrulliunuria type I
deficiency of argininosuccinate synthase
the benefit of limiting amino acid degradation
reducing the ammonia load in the urea cycle
the autosomal recessive primary hyperammonemias
type I, citrullinuria type I, argininosuccinic acidemiaargininemia
arginine synthesis is catalyzed by
argininosuccinate lyase
the rate limiting and committing step of the urea cycle is
carbamoyl phosphate synthesis
transamination
transfer of an a-amino group from an amino acid to an a-keto acid
is a precursor for the allosteric activator of the urea cycle
glutamate
the role of citrulline suppliment in type I and II hyperammonemia
to capture aspartate so at least one nitrogen can be excreted
deficiency causes citrullinuria type I
argininosuccinate synthetase
1—- + 2—- –(GDH)—> NADP+ + Glutamatemuscle and peripheral tissues
a-KG + NH4+required for glutamine transport
during transamination, the amino acid nitrogen is generally collected on
glutamate
main glutamine users
kidney, gut, immune cells and liver
Three ways to supply the amino acid pool
1- degradation of bodies own protein (endogenous)2- degradation of dietary protein (exogenous)3- synth. of non-essential aa from other pathways
glutamate indirectly provides nitrogen to urea by
transaminating oxaloacetate into aspartate. Aspartate then provides an amino group to urea.
high levels of ALT and AST in plasma indicates
liver damage
the reaction catalyzed by glutamate dehydrogenase
a-ketoglu + NH4+ glutamate
blood arginine level for type I and type II
both low
blood NH3 level for type I and type II
both high
starvation and the brain
during starvation the brain switches from glucose to ketone bodies (MAINLY FROM FATTY ACIDS) as energy source.
glutamate dehydrogenaseresults in the formation of these compound in the kidney and liver
NADPH, a-ketoflutarate, NH4+ and H+Substrate: Glutamate and HOH
Urea is transported to the —— and excreted in ——–. some urea leaves through the —–, too.
urea transported to the kidney and excreted in urine.some urea leaves through intestine
the transamination reaction is —— and ——- catalyzes the reaction.
reversible, transaminase (aminotransferase)
citrulline and aspartate form argininosuccinate. what is the source of aspartate?
aspartate is produced by transamination of oxaloacetate (AST) and the aspartate nitrogen will incorporate into urea
fasting and muscle proteins
during fasting muscle proteins are degraded and amino acids are transported to the liver and converted to glucose.And the Nitrogen of the used amino are converted to urea.
scavenger drug for glycine
benzoate + glycine –> hippuric acid –> excretion
pyridoxine
B6
treatment of urea cycle disorders
a- reduce the ammonia load on the urea cycleb- provide urea cycle intermediates
cleavage of arginine into urea and ornithine takes place in
the cytosol
the first step in urea synthesis is catalyzed by
carbamoyl phosphate synthetase I
blood ammonia in liver damage
increased
NAME?
N-acetylglutamate
amino acid degradation takes place in
all tissues
deficiency of arginase causes
argininemia
argininosuccinate synthesis is catalyzed by
argininosuccinate synthetase
arginine as a reactant for nitric oxide synthesis
Arginine +NADPH + O2 –> citrulline +NO + NADP+ + H2O
it can provide nitrogen both directly and indirectly to the urea cycle
glutamate
citrulline synthesis is catalyzed by
ornithine transcarbamoylase
the precursors of N-acetyl glutamate
glutamate and Acetyl CoA
The role of Arginine in the following reaction:Glutamate + Acetyl-CoA –> N-acetyl Glutamate
Arginine is + (activator)
ALT specificity vs AST
ALT is more specific
CPSII
the enzyme for carbanmoyl phosphate synthesis in the cytosol from glutamine and CO2
BUN and blood creatinine in kidney damage
increased
the first two intermediates of the urea cycles which are made in the mitochondria
carbamoyl phosphate and citrulline
urea cycle starts in —– and is completed in the —–.
starts in mitochondria and completed in cytosol.
the major reaction in the muscles that constitute the main source of alanine
protein degradation and transamination
AST
aspartate aminotransferase(Oxaloacetate/glutamate) and (Aspartate/a-ketoglutrate)
scavenger drug for glutamine
Phenylbutyrate
BUN, blood creatinine and blood uric acid level during pregnancy
decreased
its deficiency causes argininosuccynyl acidemia
argininosuccinate lyase
sources of alanine- alanine transport to the liver: Glucose/Alanine Cycle
main: muscle (result of protein degradation and transamination)Other: kidney and intestine (conversion of glutamine to alanine)
Blood creatinine in kidney damage
increased
scavenger drugs
conjugate amino acids and target them for urinary excretion
this vitamin is required for PLP formation
Vitamin B6- pyridoxine
The third step of urea cycle
argininoscuccinate synthesis
transports ornithine into the mitochondria from the cytosol
ornithine translocase
ornithine translocase
transports ornithine into the mitochondria from the cytosol
blood uric acid in pregnancy
decreased
conditions that resemble fasting as well as high protein diet and excessive degradation ——– urea synthesis and —— synthesis of urea cycle enzymes.
increase, increase
arginine —> urea and ornithineE: arginasethe fate of the arginine and ornithine
arginine cab be used by other pathways: protein synthesis and nitric oxide synthesisornithine moves back to mitochondria and reacts with another molecule of carbamoyl phosphate
the reactions that lead to the formation of alanine in kidney and intestine
conversion of glutamine to alanine
the reaction catalyzed by glutamine synthetase
Glutamate + NH4+ —– ATP —> glutamine
the product of transamination of oxaloacetate (AST)
aspartate
arginine synthesis takes place in
cytosol
blood uric acid in gout
increased
diagnostic tool for primary hyperammonemias
metabolites before the deficiency accumulates in blood/ urine.Metabolites after the deficiency have much lower levels.
The central role of glutamate in nitrogen removal- 3 general descriptions
precursor for allosteric activatorProvides nitrogen in two different wayscollects nitrogen
when to provide citrulline supplement as urea cycle intermediate
In type I and II hyperammonemia.it captures aspartate, so at least one nitrogen can be excreted
Three general ways to deplete amino acid pool
1- protein synthesis for the body2- consumption of aa as precursor for small nitrogen containing molecules3- conversion of amino acids to glucose, glycogen, a-Kbodies, and fatty acid oroxidation to Co2 and H2o
regulation of the urea cycle
N-acetylglutamate (allosteric activator)High arginine levelHigh protein diet and excessive degradationand the concentration of substrate and intermediates
Blood creatinine in pregnancy
decreased
arginine supplement for argininosuccinate lyase deficiency
it generates more ornithine for urea cycle to continue.also, catalyzes the production of N-acetylglutamate so acceelerates CPSI
The two main purposes for the transport of alanine to the liver
1- removal of nitrogen through the urea cycle2- glucogeogenesis
1—- + 2—– -(glutamine synthetase)–> glutamine + ADP Muscle and peripheral tissue
glutamineRequired fro glutamine transport
objFate of carbon core of amino acid depends on the nutritional state of the body.Fate of Carbon core of aa in the fed state:
Energy storageThe carbon of the excess amino acids will be converted to:1- glucose –> Glycogen2-acetylCoa –> TAG
objFate of carbon core of amino acid depends on the nutritional state of the body.Fate of Carbon core of aa in the fasting state
Energy productionCo2pyruvateTCA int.Acetyl CoA- Acetoacetate
What is common to both the fed and fasting states with respect to the fate of the carbon core of aa:
In both, amino acids are constantly used for the synthesis of physiologically important metabolites - proteins and hormones
obj ketogenic amino acids
leucine, lysine
objglucogenic aa
non essentialsAlaArgAsnAspCysGluGlnGlyPro Seress. aa.HisMetThrVal
Objnoess. aa.
AlaArgAsnAspCysGluGlnGlyPro SerTyrosine ( glucogenic and ketogenic)The rest are glucogenic
objthe glucogenic noess. aa.
AlaArgAsnAspCysGluGlnGlyPro Ser
objthe glucogenic and ketogenic noess aa.
tyr
objthe glucogenic and ketogenic ess.aa.
ThrIsoPheTrp
objconditionally ess. aa.
tyr, Arg, Cys
objThe surplus of cystine (cond. ess. aa.) comes from
met (ess, glucogenic)
objTyr (cond. ess. aa./ glucogenic and ketogenic) is produced from
phenyl-alanince (gluco-ketogenic)
objConditionally essential Arg
Arg is not ess. for adults, byt it is ess. for children
the aa that is ess for only children
Arg
Tyr production
Tyr is produced by the hydroxylation of phenyl-alanine
the source for carbon cores of 10-essentional aa.
glucose
ObjThe 10 ess. aa
Glucogenic: His, Met, Thr, Val.Gluco/Keto: Thr, ILe, Phe, TrpKet: leu, Lys
All the ketogenic aa. are
essentionalLeu, Lys
aa. syn. f. glycolysis int.
Cys, Gly, Ser, Ala
aa syn. f. OxA
Asp, Asn
aa. syn. f. a-ketoglutrate
Glu, Gln, Pro, Arg
The lonely aa.(an amino acid that is not produced via any three common pathways: f. OxA, F. a-ketoglutrjate and f. gly int.)
tyrosine, which is produced by the hydroxylation of phenylalanine.
Coenz. fo. transamination (TA) and deamination (DA)
pyridoxal-phosphate (B6)
B6
pyridoxal phosphate- a conenzyme for deamination and transamination
Coenz. fo. metabolism of Ser, Gly, Met, His
Tetrahydrofolate (folate)
Tetrahydrofolate
coenzyme fo. metabolism of gly, his, met, ser
cobalamins
B12 (Met metabolism conezyme)
B12 as a conenzyme
B12- Cobalamins is a conezyme for methionine metabolism
BH4
tetra-hydro.biopterin
tetrahydrobipterin is synthesized from
GTP
Tetrahydrobiopterine (BH4) is a conezyme for
hydroxylation of phenylalanine, tyr and trp
Hydroxylation of Phe, Tyr, Trp iis assisted by this coenzyme
BH4- tetrahydrobioptrein
The coenzyme for oxidative decarboxylation of BCAA
Thiamine-Pyrophosphate (B1) and lipoate
Thiamine-pyrophosphate and lipoate are common coenzymes for
oxidative decarboxylation of BCAA.thiamine-pyrophosphate is B1
Other names for B1, B6 and B12
B1- thiaminepyrophosphateB6- pyridoxal phosphateB12 cobalamins