Exam 2 Peng 2 Flashcards
what are the two main ways to degrade AA?
1) transamination
2) oxidative deamination
transamination is typically the first step in?
catabolism of AA
is transamination reversible? catalyzed by?
Yes reversible; catalyzed by aminotransferase
transamination produces?
glutamate
What happens in transamination?
- *alpha-ketogluterate accepts the amino group from AA and becomes glutamate
- *AA loses amino group and becomes alpha-keto acid
biological importance of transamination?
AA gives up amino group (CONTAINS NITROGEN) to form glutamate which is a common substrate! Now the body only needs ONE step oxidative deamination
again, aminotransferases catalyze?
the transfer of alpha-amino groups to glutamate in transamination of AA; substrate specificity! many transfereases wont work on different AA
what are the two most important aminotransferases?
1) asparate aminotransferase -asparate and alpha-ketogluterate= oxaloacetate and glutamate
2) alanina aminotransferase - alanine + alpha-gluatarate = pyruvate + glutamate
What are good markers for liver diseases in the urine?
asparate aminotransferase and alanine aminotransferase because they are typically restricted to liver cells
all aminotransferases require?
coenzyme pyridoxal phosphate
what is coenzyme pyridoxal phosphate?
it is the coenzyme required by aminotransferase, derived off vitamin B6
what is aminotransferases equilibrium constant? This means?
near 1. means it is HIGHLY reversible
is oxidation deamination reversible? What type of reaction is it?
highly reversible; redox reaction (leo ger)
what happens in oxidative deamination?
amino groups are liberates off glutamate as free ammonia; this is catalyzed by glutamate dehydrogenase mitochondrial enzyme
what is oxidative deaminations coenzyme?
nicotinamide adenine dinucleotide
what is nicotinamide adenine dinucleotide?
- the oxidator in oxidative deamination
- coenzyme for oxidative deamination
- phosphorylated and reduced form used in reversed rxn
what is released in oxidative deamination?
NH3 which is turned into NH4 and converted to urea
what is the issue with the creation of NH3 and NH4 in tissue other than the liver? how is this overcome?
it is toxic and must be kept at low levels in the blood. it is overcome y transporting nitrogen as alanine and glutamine in the blood, which are NON TOXIC
how do you get alanine and glutamine as transporters?
1) glutamine cycle- glatamate combines with ammonia to form glutamine catalyzed by glutamine synthase
2) glucose alanine cycle- glucose is converted to pyruvate which is converted to alanine and released into blood
* *once glutamate and alanine reach the liver, they are deaminated down to ammonia again, peed out as uria
what makes alanine and glutamine such good carriers of nitrogen?
muscles cells have lots of glucose to convert alanine and glutamine is literally glutamate with extra amine group
what are the building blocks of urea?
C and O come from CO2 and water; one N from NH3 and the other from aspartate
excess ammonium (NH4) is converted?
into urea by the urea cycle; major dispoal form of AA (90% of nitrogen in urine)
urea is a nontoxic form of?
nitrogen
sources of ammonia (NH3)?
1) AA deamination
2) plasma glutamine
3) bacterial action in the intestine (urease)
4) amines in the diet
5) catabolism of purines and pyrimidines
where does glutamines formation from glutamate occur?
BRAIN, cns, liver, muscle
glutamine is found where in higher concentrations than other AA?
plasma
what is hyperammonenia?
elevated level of ammonia (NH3) in blood due to acquired liver disease or genetic defects in urea cycle
*if genetic= very fatal after 1 day of birth, treatment is protein restriction
ammonia is especially toxic to?
CNS aka brain = coma or death
with kidney failure, plasma urea increases through the action of?
intestinal bacteria urease leading to hyperammonia
treatment of hyperammonia?
restiction of dietary protein
1) phenylacetate (binds and excretes glutamin)
2) antibiotics (suppress the action of intestinal bacteria urease)
5 steps in urea cycle?
1) formation of carbamoyl phosphate from bicarbonate
2) formation of citrulline
3) synthesis of arginosuccinate
4) cleavage of arginiosuccinate
5) cleavage of arginine to ornithine and urea
urea cycle is regulated by?
both substrate availbility and enzyme activity/availbility
urea is transported from the liver? via?
liver to the kidney via blood and filtered and excreted in the urine
where do the urea cycle steps occur?
1 and 2 in mitochondrial matrix, 3 in cytosol, 5 exclusively in liver
what is stoichiometry of the urea cycle?
asparate +NH3+ HCO3+ 3ATP+ water –> urea, fumarate +2 ADP + AMP +2Pi + PPi (2 orthophosphate and 1 pyrophosphate)
what steps in the urea cycle require energy?
1 uses 2 ATP and 3 uses 1 ATP
= 3 ATP total
