chp 25 nitrogen acquisition and amino acid metabolism

microorganims acavenge amino acids from their __________ for fuel when needed

environment

herbibores require ________ amount of energy from amino acids

small

plants and usage of amino acids as fuel source

do not use them for fuel but degrade them to form other metabolites

carnivores and amino acids as fuel

get 90% of energy needs from AA’s

under what 3 circumstances do amino acids undergo oxidative catabolism

1. leftover amino acids from normal protein turnover are degraded

2. amino acids from diet that exceeds body’s needs are degraded

3. proteins in body broken down to supply amino acids for energy when carbs are scarce

where does digestion of proteins begin

stomach

protein entering stomach stimulates secretion of what

gastrin what

gastrin stimulates secretion of what 2 things

• HCL to decrease pH

• pepsinogen

pepsinogen is converted into what

pepsin

what does pepsin do

cuts protein into peptides in the stomach

in the stomach we go from proteins to

peptides

where are peptides then hydrolyzed into amino acids

small intestines and pancreas

how is acidic content from stomach neutralized

secretion of secretin which stimulates bicarbonate release from pancreas

presence of AA in small intestines causes what to be released

cholecystokinin (CCK)

CCK does what

stimulates pancreatic enzyme release (trypsinogen, chymotrypsinogen, procarboxypeptidases A and B)

(also secretes bile for lipids)

what other macro also causes CCK to be released

lipids

what converts trypsinogen into trypsin

enteropeptidases (as they do proteolytic cleavage)

trypsin activation activates what enzymes

chymotrypsinogen, procarboxytidases, prelastasem and more trypsin

function of pepsin, trypsin and chymotrypsin, and aminopeptidases and carboxypeptidases

-pepsin will break down proteins into peptides

- trypsin and chymotrypsin will break peptides into small peptides

-aminopeptidases and carboxypeptidases will break down the small peptides into amino acids

the free amino acids go where (from IS to what organ)

into SI epithelial cells —> enter capillaries—> and are taken to liver

why do we have zymogens

because pancreas holds most of our enzymes and if they were active would cause harm to pancreas

what is pancreatic trypsin inhibitor

released by pancreas to prevent autodigestion of pancreas

BECAUSE TRYPSIN ACTIVATES MOST OF THE PANCREATIC ENZYMES

by what are zymogens activated in SI

trypsin

protein degration from stomach to SI cells

Parietal cells release HCL, chief release pepsinogen, and gastric mucosa release gastrin all to start the digestion. In the stomach, the pepsinogen is turned into pepsin (most important) to begin the digestion. Then these will go to the duodenum, and will have bicarbonate released to raise the pH. Then pancreas releases zymogens to continue digestion which are activated. Then when we have amino acids, we absorb them

pathway of nitrogen metabolism picture

how are amino acids stored in body

they are not, so proteins are continuously undergoing protein turnover (biosynthesis and degradation)

since amino acids not really stored, how do animals get nitrogen

continuously replenish supply through diet, but if not enough then will use muscle protein (but wont be replenished)

fates of nitrogen in organisms (plants, aquatic vertebrates, terrestial vertebrates and sharks, birds and reptiles, HUMANS )

• plants- conserve almost all nitrogen

• aquatic vertebrates release ammonia to environment

• aquatic vertebrates, terrestrial vertebrates and sharks excrete ammonia as urea

• birds and reptiles excrete nitrogen as uric acid (pasty)

• humans excrete urea (from AA) and uric acid (from purine catabolism)

humans do what to nitrogen (how excreted)

urea and uric acid

ammonia is what are high levels

toxic

all organisms assimilate NH3 via reactions yielding (what 4 molecules is NH3 possibly turned into

1. glutamate

2. glutamine

3. asparganine

4. carbamoyl phosphate

what 2 amino acids are the collecting point for NH2

glutamine and glutamate

in most tissues, what occurs to NH4+

is transferred to glutamate to form glutamine which can then enter the liver and be turned into glutamate again and release NH4+ to urea cycle

in skeletal tissue (muscle) what occurs to NH4+

NH2 is transferred to pyr to form ala, which is transported to the liver and the amino group is transferred to αKG to form glu

the glu can then release NH4 for urea

in liver, what occurs to NH4+

• AA transfer of NH2 to αKG to form Glu,

• Enters the mitochondria to release NH4+ (enzymatic transamination)

what is the first step in degradation of amino acid

removal of amino group

how is the amino group of AA first removed

through enzymatic transamination

what is transamination

removal of amino group from amino acid and transferring it to keto acid, which will make the amino acid a keto acid and the keto acid an amino acid

what enzymes do transamination

aminotransferases

what do aminotransferases require

cofactor PLP (piroxal phosphate)

PLP is derived from

B6 vitamin

what typically accepts the amino group

alphaKG (because when it accepts amino group it becomes glutamate)

what can act as temporary storage of nitrogen

L-glutamine (can donate the Amino group when needed for AA biosynthesis or amino group can be converted to urea)

aminotransferases are high in what tissue

liver

L-glutamate can function as what for what 2 pathwaysb

amino group donor for biosynthesis pathway OR excretion pathways

because it carries an amino group that can be used to make amino acid or released to go to urea cycle

PLP serves as what

coenzyme for aminotransferases (from B6)

what are the 3 metabolic fates of ammoniun (3 enzymes perform the 3 reactions that could occur)

1. carbamoyl phosphate dehydrogenase (ammonium—> carbamoyl P)

2. glutamate dehydrogenase (glutamate to alphaKG by removal of NH4 and usage if NAD or NADP+)

3. glutamine synthetase (glutamate to glutamine by adding NH4)

carbamoyl phosphate synthetase 1 (does what, ATP needs)

will convert ammonia into carbamoyl phosphate (prep of urea cycle)

2 ATP needed (one to activate bicarbonate and one to phosphorylate carbamate)

what does glutamate dehydrogenase do

reductive amination (add amine) to alpha ketoglutarate to form glutamate OR remove amino group from glutamate to form alpha-ketoglutarate and ammonia (NH4+)

-uses NAD or NADP

what does glutamine synthetase do

ATP dependent amination glutamate to glutamine

after enzymatic transamination in liver, what must happen to ammonia (what amino acid must do so)

Glutamate must dispose of it (since glutamine is carrying the ammonia group as NH3+)

amino acids are converted into what amino acid during transamination to be able do urea cycle

glutamate

ammonia collected in glutamate is removed by what enzyme

glutamate dehydrogenase

the process of removing the ammonia from glu is what process

oxidative deamination

glu dehydrogenase uses what

NAD+ or NADP+ as electron acceptor (to remove a H and make intermediate)

the ammonia released is then processed into what

urea

the pathway for ammonia excretion therefore includes what 2 processes

transdeamination= transamination + oxidative deamination

• Transamination to get amino acid into glutamate

• Oxidative deamination to remove ammonia from glutamate and make alpha-ketoglutarate

where does oxidative deamination occur in liver cell

mitochondrial matrix

how is ammonia transported from tissues into the liver

in glutamine

the ammonia (NH4+) from intestines and kidneys can go directly to what organ

liver

other tissues have ammonia added to what to form what to be transported

add ammonia to glutamate to make glutamine (by glutamine synthetase)

• rmb that glutamine has 2 amino groups

what enzyme makes glutamine

glutamine synthetase (adds amino group)

what happens to the glutamine

it is deaminated to make glutamate and release ammonia

where is glutamine deaminated (what tissues)

intestines, kidneys, and liver

what enzyme is the enzyme that does oxidative deamination

glutamate dehydrogenase

once we have glutamate, it undergoes what (process and enzyme)

further deamination to release the other amino group ads ammonia by glutamate dehydrogenase

glutamate can also donate ammonia to what molecule when exercising in muscle

pyruvate (to make alanine)

vigorous exercise operates using what respiration type and relies on what pathway for energy

anaerobic

glycolysis

glycolysis yields what compound

pyruvate

during exercise, pyruvate is converted into what

lactic acid

to prevent build up of lactic acid in muscle, we can turn pyruvate into what

alanine to be taken to liver

the NH2 from muscle is transported to the liver in what form (what molecule)

alanine

what is the glucose alanine cycle

cycle where we have muscle protein broken down to give ammonia which then is made to glutamate —> glutamate will donate the amino group to pyruvate to make alanine—> alanine can go to liver to be made back into pyruvate—> into glucose—> back to muscle—> undergo glycolysis to make pyruvate and cycle restarts

what cycle removed ammonia from body

urea cycle

urea cycle turns ammonia into what

urea

where does the ammonia enter from originally

from glutamate, alanine, or glutamine —> but all is converted into glutamate to start process

glutamate in liver releases ammonia how (process and enzyme)

oxidative deamination by glutamate dehydrogenase

what is the only tissue that can produce urea

liver

where in cell does urea cycle occur

some in mitochondria and most in the cytosol

• mitochondria is prep and 1

• citosol is step 2-4

when glutamate is deaminated by glutamate dehydrogenase, what happens to the ammonia

it will react with bicarbonate to form carbamoyl phosphate

since glutamate was made through transamination and oxidative deamination, collectively the formation of deaminated glu is called what

transdeamination

glutamate dehydrogenase can use what electron acceptors

NAD+ or NADP+

steps of the urea cycle (substrates, products, enzyme if known)

• prep: ammonia + bicarbonate —> carbamoyl phosphate

  • by carbamoyl P synthetase (requires 2 ATP and occurs in mitochondria; first amino group entering cycle)

• 1. ornithine + carbamoyl P —> citrulline (in mitochondria)

• 2. citrulline undergoes 2 part reaction

  • citrulline —> citrullyl AMP (use ATP—> PPi= equal to 2 ATP)

  • citrullyl AMP —→ arginosuccinate (by adding aspartate with our seconds amino group)

• 3. arginosuccinate —> arginine (releasing fumarate)

• 4. arginine —> ornithine (RELEASES UREA)

• ornithine taken into mitochondria to start cycle again

before we can begin the urea cycle, the prep stage does what (enzyme, reaction, ATP)

carbamoyl P synthase recaptures the ammonia released by glutamate and adds it to bicarbonate to make carbamoyl phosphate

• this requires 2 ATP

is carbamoyl phosphate synthase regulated or not

yes

after we make carbamoyl phosphate what is the next reaction

carbamoyl phosphate will combine with orthenine to make citrulline in the mitochondria still

after citrulline is taken to the cytosol, what reactions occurs next in the urea cycle

2 part reaction

• citrulline —> citrullyl- AMP (uses 2 ATP)

• citrullyl- AMP —> arginosuccinate (has addition of aspartate with 2nd amino group)

so far, how many ATP have been used in the urea cycle

4 ATp

• 2 from prep (carbamoyl P synthase)

• 2 from step 2 (citrulline —> arginosuccinate)

at what points does amino groups enter the urea cycle

1. carbamoyl phosphate

2. aspartate

after we get arginosuccinate, what occurs in urea cycle

has fumarate taken off and becomes arginine

after we have arginine, what occurs

we release UREA and make ornithine

in what step do we make urea to be excreted

step 4 (arginine —> ornithine by releasing urea)

what is the TOTAL energy cost of urea cycle

4 ATP

• 2 ATP required for the formation of carbamoyl P

• 2 ATP required for the formation of argininosuccinate

BUT, what is also made in the urea cycle that can provide energy

fumarate

fumarate ends up going to ETC and provides how much ATP

2.5

So what is NET ATP required for urea cycle

1.5 ATP

what allosterically activates carbamoyl phosphate synthetase

N-acetylglutamate (made from glutamate and acetyl CoA)

regulation of the urea occurs in the _______ and ________ term

long and short

what molecule does short term regulation

N-acetylglutamate (by activating carbamoyl phosphate synthetase 1

how is N-acetylglutamate made

by N-acetylglutamate synthetase in the liver

• done by putting glutamate and acetyl CoA together