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nitrogen metabolism
ugki
62
Biochemistry
Professional
01/06/2012

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Term
Importance of ntirogen metabolism
Definition
major contributor to living systems

key component of aa, nucleotieds

biological useful forms are scarce
most living organisms need reduced nitrogen form
Term
Nitrogen cycle
Definition
N2 is converted to Ammonia by bacterial fixation

Ammonia is used to synthesize aa in body

Biomolecules are degraded to Ammonia and excreted

The ammonia is nitrited by soil bacteria to Nitrite

Nitrite is nitrated by soil bacteria to form Nitrate

Some nitrates will be denitrated by soil bacteria to N2 others will be reduced by anerobic bacteria (plants) to Ammonia
Term
Ammonia incorporated into biomolecules through
Definition
glutamate and glutamine

these are 2 orders higher in mag than any other aa

can now donate amino grp to make other aa

2 step reaction glutamate + NH4 yields glutamine
Term
glutamine synthetase
Definition
found in all organisms main regulatory enzyme of nitrogen metabolism catalyzes reaction of glutamate to glutamine
Term
glutamate synthesis
Definition
alpha ketoglutarate and glutamine and NADPH yields 2 glutamate +NADP

by glutamate synthase; not present in animals
Term
minor glutamate synthesis pathway
Definition

catalyzed by glutamate dehydrogenase all organisms alpha-ketoglutarae + NH4 + NADPH yields glutamate + NADP reverse source of NH4 for the urea cycle

enzyme located in the mito matrix

Term
Allosteric regulation of glutamine synthetase
Definition
glycine, Alanine, Glucosamine-6P, Histidine, CTP, Carbamoyl phosphate, Tryptophan, AMP work synergisticly to obtain effect
Term
Covalent Regulation of Glutamine Synthetase
Definition
both adenylation and deadenylation of glutamine synthetase by adenyltransferase at Tyr397 (ade inhibits)
Term
Regulation of Adenylyltransferase for glutamine synthetase
Definition
regulated by binding of regulatory protein P11

the activity of P11 is regulated by uridylyltransferase (UT)

Pii-ump stimulates deadenylation of glutamine synthetase
Term
Uridylylation of Pii regulation
Definition
inhibited by binding of glutamine and Pi to UT

stimulated by binding of alpha-ketoglutarate and ATP to Pii
Term
glutamine synthetase regulation by gene expression
Definition
uridylylated Pii mediates the activation of transcription of the gene encoding glutamine synthetase increasing cellular concnetration of the enzyme

deuridylation of Pii does the opposite
Term
biosynthesis of glutamate in animals
Definition
transamination of alpha-ketoglutarate during amino acid catabolism

carried out by aminotransferases

prosthetic group= PLP

the opposite reaction serves as a universl source of aa through transamination reactions
Term
pyridoxal phosphate
Definition
PLP the coenzyme form of pyridoxine (vitamin B6)
Term
key chemical rearrangements in biosynthesis of aa
Definition

1. transamination reactions by enzymes containig PLP

 

2. transfer of 1C group by tetrahydrofolate or SAM

 

 3. transfer of amino groups derived from the amide nitrogen of glutamine

Term
mechanism for glutamine amidotransferases
Definition
2 domains glutamine-binding domain and NH3 acceptor domain

glutamine in GBD is attacked by cys in active center hydrolates NH2 making the intermediate

NH3 flows through channel where it reacts with the acceptor to form the aminated product
Term
alpha-ketoglutarate derived aa
Definition

glutamate glutamine proline arginine From CAC

 

alpha- PREQ

Term
3-Phosphoglycerate derived aa
Definition

Serine Glycine Cysteine from glycolysis

 

3PB=SCG

Term
oxaloacetate derived aa
Definition

aspartate asparagine methionine threonine lysine from CAC

 

DONT K M

Term
Pyruvate derived aa
Definition

Alanine Valine Leucine Isoleucine from glycolysis

 

PAVIL

Term
PEP and erythose 4-phosphate derived aa
Definition
tryptophan
phenylaline
tyroxine

from glycolysis and PPP
Term
Ribose 5-phosphate derived aa
Definition
histiine by PPP
Term
Essential Amino Acids
Definition

Must be obtained from food Valine Leucine Isoleucine Tryptophan Phenylaline Histidine Methionine Threonine Lysine

 

WTFMHVIL

Term
Conditionally essential amino acids
Definition

required to some degree in young, growing or ill animals glutamine proline arginine glycine cysteine tyrosine

 

QYCGPR

Term
5-phosphorylbosil-1-pyroposphate (PRPP)
Definition
a key intermediate in several pathways of amion acids and nucleotide biosynthesis

links them

synthesized from ribose-5-phosphate from PPP

catalyzed by enzyme ribose phosphate pyrophosphokinae
Term
Proline synthesis
Definition
from glutamate

key intermediate is glutamate gamma semialdehyde
Term
Arginine to Proline
Definition
arginase converts arginine to ornithine and urea

ornithine is converted to glutamate-gamma-semialdehyde by ornithine delta-aminotransferase
Term
Pathway to biosynthesis of arginine in mammals
Definition
ornithine delta-aminotransferase operates in the direction of ornithine formation

converted to citrulline and arginine in the urea cycle
Term
Serine production
Definition
from 3-Phosphoglycerate

glutamate transfers amino group and releases alpha-ketoglutarate
Term
Glycine production
Definition

From serine by serine hydroxymethyltransferase removes a carbon from serine can be produced in liver of vertebrates from CO2 and NH4 with N5N10-MEthyleneH4folate this releases tetrahdyrofolate

cofactor= PLP needs H4folate

Term
Serine hydroxymethyltransferase
Definition
requires H4folate to remove a carbon from serine

accepts the beta carbon of serine and forms a methylene bridge btw N5 and N10 to yield N5,N10 methylenetetrahydrofolate
Term
Cysteine production
Definition
from serine and homocysteine

methionine furnishes the sulfur group and serine supplies the carbon skeleton
Term
homocysteine production
Definition
made from methionine via SAM and SAHC
Term
Aspartate production
Definition
amiontransferase reaction of oxaloacetate and glutamate to form alpha-ketoglutarate and aspartate
Term
Alanine production
Definition
amiontransferase reaction of pyruvate and glutamate forming alpha-ketoglutarte and alanine
Term
Asparagine production
Definition
synthesized by amidation of aspartate with glutamine donating the NH4+ through asparagine synthetase
Term
Methionine, threonine and lysine production
Definition
aspartate gives rise to these

branch pt occur at aspartate beta-semialdehyde and homoserine
Term
isoleucine production
Definition
comes from pyruvate and threonine
Term
Valine produciton
Definition
shares 4 enzymes with isoleucine

made from pyruvate
Term
Leucine
Definition
starting pt from alpha-ketoisovalerate an intermediate from the valine pathway

this will then proceed 4 more steps to leucine
Term
Aromatic Amino acids
Definition
animals do not have these and obtain them from food

2 PEP and 1 erythrose 4-phosphate will make chorismate

will give phenylaline, tyrosine, tryptophan
Term
Chorismate
Definition
key common intermediate in bosynthesis of tryptophan, tyrosine, and phenylalanine
Term
tyrosine production
Definition

from phenylalanine through oxidation by phenylalanine hydroxylase and tyrosine can go to melanin, catecholamines, fumarate, and tissue proteins

 

can come from chorismate

Term
Phenylketonuria (PKU)
Definition
deficiency of phenylalanine hydroxylase

instead of phenylaline forming tyrosine it will form phenylpyruvate

phenylpyruvate can be converted to phenyllactate and phenylacetate all toxic substances

CNS: mental retardation, hyperactivity, seizures
hypopigmentation
Term
Histidine production
Definition
derives from 3 precursors

PRPP- contributes C skeleton
ATP- contributes N and a carbon
Glutamine supplies second ring N

ATP acts as a metabolite not energy factor

3 step process:
1. condensation of ATP and PRPP
2.purine/ ribose ring opening leads to N15-Phosphoribulosyl-formimino-5-aminoimidazole-4-carboxamide ribonucleotide

then the formation f the imidazole ring through use of glutamine

AICAR is released and histidine is formed
Term
Sequential feedback inhibition
Definition
interlocking regulatory mechanisms in the biosynthesis of several aa so if 1 enzyme in the system is halted the previous enzymes are also halted
Term
enzyme multiplicity in aa biosynthesis
Definition
prevents one biosynthetic end product from shutting down key steps in a pathway when other products of the same pathway are required
Term
Amino Acids are precurosors for
Definition
hormones, coenzymes, nucleotides, alkaloids, cell wall polymers, porphyrins, antibiotics, pigments and neurotransmitters
Term
AA role in creatine production
Definition
synthesized from glycine, arginie and methionine in the form of SAM

glycine + arginine in amidinotransferase then add SAM for a methyl donation to form creatine
Term
Phosphocreatine
Definition
an energy buffer in skeletal muscle

formed from the additon of ATP to creatine by creatine kinase
Term
AA role in glutathione production
Definition
gamma-carboxyl group of glutamate and alpha-amino group of cysteine are condensed with ATP

alpha carboxyl of cystein then to glycine with ATP to form Glutathione
Term
Glutathione
Definition
serves as a redox buffer,
maintaining sulfhydryl groups of proteins in the reduced state
the iron of heme in the ferrous state
reducing glutaredoxin in deoxyribonucleotide synthesis

redox function used to remove toxic peroxides
Term
glutathione peroxidase
Definition
enzyme used to catalyze the redox function of glutathione in peroxide removal

contains selenocystein for enzymatic activity
Term
Catecholamine synthesis
Definition
(dopamine > norep > epi)

from tyrosine

important cofactor in this process is PLP and enzyme aromatic amion acid decarboxylase
Term
GABA synthesis
Definition
from amino acid glutamate by decarboxylation

cofactor is PLP enzyme is glutamate decarboxylase
Term
Serotonin synthesis
Definition
from the aa tryptophan

2 step process needs the aromatic aa decarboxylase enzyme and cofactor PLP
Term
biosynthesis of histamine
Definition
from aa histidine

decarboxylatd by histidine decarboxylase; cofactor PLP
Term
Cimethidien
Definition
strucutral analog of histamine

prominent example of histamine receptor antagonist

promotes healing of duodenal ulcers by inhibitng secretion of gastric acid
Term
Biosynthesis of nitric oxide
Definition
from aa arginine

plays a role in neurotransmission, blood cloting and blood pressure

2 steps are catalyzed by nitric oxide synthase

reaction is a 5e oxidation

4 cofactors FMN, FAD, tetrahydrobiopterin and Fe3+ heme
Term
nitric oxide synthase
Definition
dimeric enzyme structurally related to NADPH cytochrome P-450 reductase
Term
Spermine and Spermidine biosynthesis
Definition
involved in DNA packaging derived from methionine and ornithine

1. decarboxylation of ornithine by PLP (ornithine decarboxylase) forming putrescine

2.SAM then acts as a source of proplyamino groups transfer onto putrescine

3. catalyzed by propylaminotransferase I and II to form spermidine then spermine
Term
Treating African Sleep Sickness
Definition
includes the use of mechanism-based suicide enzyme inactivators

targets polyamine biosynthesis in Trypanosoma cells (protist)

target is ornithine decarboxylase blocked by DFMO
Term
DFMO
Definition
structural analog of ornithine

inhibitor of ornithine decarboxylase

acts by providing an alternative electron sink in the form of 2 strategically placed flourine atoms

S of a Cys forms a covalent complex with the highly reactive PLP-inhibitor adduct in an essentially irreversible reaction
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