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Week 13- SHANE > Amino Acid Degradation and Synthesis II > Flashcards

Amino Acid Degradation and Synthesis II Flashcards

1
Q

What is the major carrier of nitrogen in the blood?

A

glutamine

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2
Q

What is glutamine made from for transfer?

A

NH4+ is added to a-ketogluterate (through ATP and NADPH) to make glutamine, which then goes to the liver from peripheral tissue where it is deaminated twice to give off NH4+ to reform a-keotgluterate

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3
Q

What is the fate of the Nh4+ groups given off during the reconversion of glutamine to a-ketogluterate in the liver?

A

made into urea and eventually urine

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4
Q

What is another nitrogen transporters that gives nitrogen products to the production of urea?

A

alanine (gives off NH3). In the alanine cycle, alanine goes to the liver from peripheral tissue in fasting conditions and the ALT enzyme trans-aminates alanine to pyruvate (for gluconeogenesis) which causes NH3 to be given off. Most of the NH3 enters the urea cycle

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5
Q

Alanine and glutamine pass their AAs to what compound for them to enter the urea cycle?

A

glutamate

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6
Q

What are the significances of NH4+ and NH3 in the urea cycle?

A

NH4+ is the predominant form of ammonia in the body due to its high dissociation constant (9.3), but NH3 is important because it is the form that can cross cell membranes (NH4+ cannot because it is charged)

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7
Q

T or F. High levels of ammonia can be toxic

A

T. Normal level of ammonia in blood = 30-60 mM

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8
Q

The majority of nitrogen in urine is present in what form?

A

urea

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9
Q

Where does the urea cycle occur?

A

some steps in mitochondria and some in the cytosol. ALL in the liver

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10
Q

What is the first step in the urea cycle?

A

HCO3- made from H2O and Co2 is combined with NH4+ to form carbamoyl phosphate (through input of 2 ATP)

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11
Q

What enzyme catalyzes the conversion of HCO3- and NH4+ to carbamoyl phosphate?

A

carbamoyl phosphate synthetase I (CPSI)

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12
Q

What is the second step in the urea cycle?

A

carbamoyl phosphate is combined with ornithine to make citrulline (by giving off a phosphate group)

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13
Q

What enzyme catalyzes the conversion of carbamoyl phosphate and ornithine to citrulline?

A

ornithine transcarbamoylase (OTC)

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14
Q

What happens to the citrulline?

A

it moves OUT of the mitochondria into the cytosol (via exchange of ornithine into the mitochondria)

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15
Q

What is the source of the second nitrogen in urea (remember that NH4+ from glutamine/alanine is the first)?

A

aspartic acid (aspartate)

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16
Q

What happens to the citrulline once in the cytosol?

A

it combines with aspartic acid (via ATP input) to form argininosuccinate

(enzyme is argininosuccinate syntheses)

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17
Q

What happens to argininosuccinate?

A

it splits up to form fumarate and arginine as part of the Krebs Bi-cycle (via the enzyme argininosuccinate lyase)

fumarate then enters the TCA and arginine continues along the urea cycle

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18
Q

What happens to the arginine?

A

it is converted to ornithine by giving off urea (via the enzyme arginase). The ornithine is then transferred back to the mitochondria (via exchange with citruline leaving) and then can be re-used in the next cycle (via combo with carbamoyl phosphate)

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19
Q

How do you measure the urea cycle?

A

BUN- blood urea nitrogen (normal 250-700 uM)

high BUN= renal failure
low BUN= deficient urea cycle

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20
Q

What is the most common deficiency of the urea cycle?

A

OTC deficiency

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21
Q

What is OTC deficiency?

A

x linked disorder
results in high ammonia levels in the blood, high rotate (orotic acid), and low citrulline

which can lead to neuronal damage and mental retardation

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22
Q

What happens to carbamoyl phosphate when there is an OTC deficiency?

A

it will be converted to orotate which is used from pyrimidine synthesis

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23
Q

What is the treatment for OTC deficiency?

A

Need early intervention. Generate low nitrogen levels by:
1) Low-protein diet

2) Drugs that conjugate (react with) amino acids
- Benzoic acid and phenyl butyrate. Conjugated AAs are then lost by excretion

-Nitrogen used to resynthesize amino acids that are lost

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24
Q

What is the main source of arginine in the body?

A

the urea cycle

25
Q

How is tyrosine made?

A

phenylalanine via phenylalanine hydroxylase (adds a hydroxyl group)

26
Q

What cofactor does phenylalanine hydroxylase use?

A

tetrahydrobiopterin (BH4)- synthesized by GTP

27
Q

Blocking the action of phenylalanine hydroxylase causes what?

A

PKU- phenylketonuria (inreased levels of Phe)

deficiency in the synthesis of BH4 can also cause PKU

28
Q

What happens to tyrosine once synthesized?

A

it can be converted to p-hydroxyphenolpyruvate via tyrosine aminotransferase

29
Q

A block in tyrosine aminotransferase can lead to what?

A

Tyrosinemia II- can lead to neurological problems

30
Q

What cofactor does tyrosine aminotransferase II use?

A

PLP (paradoxyl phosphate)

31
Q

What is the treatment for Tyrosinemia II?

A

diets/foods low in phenylalanine and tyrosine

32
Q

What happens to p-hydroxyphenolpyruvate once synthesized?

A

it can be made into homogentisate

33
Q

What happens to homogentisate once synthesized?

A

it is further converted via homogentisate oxidase (product unimportant)

34
Q

A block in the activity of homogentisate oxidase leads to what?

A

Alcaptonuria

35
Q

What is a clinical sign of alcaptonuria?

A

urine forms a dark pigment when exposed to air

can lead to arthritis

36
Q

What is Tyrosinemia I?

A

a disease caused by a block in the activity in fumarylacetoacetate hydrolase (which catalyzes the final step in the phenylalanine/tyrosine pathway from an intermediate to fumarate and acetoacetate

37
Q

How is alanine made?

A

transamination from pyruvate

38
Q

How is serine made?

A

from 3-phosphoglycerate (a glycolysis intermediate) or from glycine

39
Q

What glycolysis intermediate can serine be made into?

A

2-phopshoglycerate

40
Q

How can glycine be made?

A

serine can be converted to glycine via serine hydroxymethyl transferase (rxn is reversible)

41
Q

What cofactors does serine hydroxymethyl transferase use?

A

PLP and tetrahydrofolate (FH4)

42
Q

What is FH4?

A

tetrahydrofolate is the reduced form of folic acid (folate)- reduced form is the most common in the body

43
Q

What is folate used for?

A

glycine synthesis, nucleotide metabolism, and transfer of carbon to vitamin B12

44
Q

How is cysteine made from serine?

A

homocysteine is added to serine using PLP to make cystathionine, which can react with PLP to form cysteine

45
Q

Vitamin B12 is aka?

A

cobalamin- coordinated cobalt

obtained from meat, eggs, dairy, fish

46
Q

What does vitamin B12 do?

A

cofactor for 2 rxns:
1) transfer of methyl group from FH4 to homocysteine to form methionine

2) rearrangement of methylmalonyl-CoA to generate succinyl-CoA

47
Q

How can homocysteine be made from methionine (essential and obtained from diet?

A

via conversion to s-adenylomethionine (SAM) (using ATP and giving off phosphate groups) and then conversion to s-adenylohomocysteine (SAH) by SAM giving off a methyl group. SAH is then converted to homocysteine by giving off adenosine

48
Q

What does FH4 do in terms of homocysteine and methionine?

A

FH4 can transfer a methyl group to vitamin B12 which can then pass the methyl group to homocysteine to form methionine

49
Q

What is homocysteinemia?

A

high homocysteine levels in the blood

describes a biochemical state- not a specific disease

high levels of homocysteine will also lead to homocystinemia and homocystinuria and high levels of methionine in the blood (homocysteinuria NOT observed)

high levels an be a good diagnostic marker for cardiovascular disease (maybe better than LDL)

50
Q

What is the classical cause of homocysteinemia?

A

deficiency in cystathionine B-synthase (CBS) enzyme used to produce cystathionine (and eventually cysteine)

can also be caused by deficiency in the cofactors involved (FH4 and vitamin B12)

51
Q

What is homocystine?

A

two homocysteine molecules connected by sulfide bonds (will have high levels with homocysteinemia

52
Q

What are common homocysteinemia clinical manifestations?

A

pathology is variable

dislocated optic lens (interfere with collagen function), abnormal blot clotting

53
Q

What is the treatment for homocysteinemia?

A

low methionine diets and oral vitamin B6 (which is a precursor for PLP)

54
Q

How do you make glutamate?

A

transamination with a-ketogluterate

55
Q

How do you make glutamine?

A

glutamate + NH4

56
Q

How do you make aspartate?

A

transamination with OAA

57
Q

How do you make asparagine?

A

aspartate + glutamine

58
Q

How do you make proline?

A

from glutamate

Week 13- SHANE (12 decks)

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