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Amino Acid Metabolism Flashcards

1
Q

How can carbon skeletons from aa enter TCA cycle (as which intermediates)?

A
  • acetyl coA
  • alpha-ketoglutarate
  • succinyl coA
  • fumarate
  • OAA
  • pyruvate
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2
Q

what is FH4?

A

tetrahydrofolate

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3
Q

what is BH4?

A

tetrahydrobiopterin

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4
Q

what is PLP?

A

pyridoxyl phosphate - B6

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5
Q

what is the only organ to have all enzymes for aa synthesis and breakdown?

A

liver

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6
Q

glucogenic vs. ketogenic

A

glucogenic: contribute to blood glucose levels
ketogenic: does not

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7
Q

what aa’s are purely ketogenic?

A

Leu

Lys

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8
Q

what aa’s are both ketogenic and glucogenic?

A 
Ile
Thr
Phe
Tyr
Trp
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9
Q

what aa’s are purely glucogenic?

A

everything except Lue, Lys, Ile, Thr, Phe, Tyr, Trp

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10
Q

fates of L,V,I,A,Q,D

A 
L: ketogenic
V: glucogenic
I: both
A: glucogenic
Q: glucogenic
D: glucogenic
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11
Q

which central pathways are aa carbons converted to intermediates of?

A
  • glycolytic pathways
  • TCA
  • lipid metabolism
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12
Q

what is the first step of aa metabolism?

A

transamination - transfer alpha amino group to a-KG or OAA, providing Glu and Asp (N for urea cycle)

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13
Q

which aa cannot undergo transamination?

A

Lys

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14
Q

ketogenic products of ketogenic aa’s?

A

acetyl coA -> Thr, Lys, Ile, Trp
HMG-coA -> Leu
acetoacetate -> Phe, Tyr

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15
Q

how do all of the ketogenic products of aa’s contribute to ketone body synthesis (pathway)?

A

acetyl coA + acetoacetyl coA -> HMG-coA -> acetoacetate (ketone bodies)

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16
Q

treatment for ALL

A

asparaginase - reduce serum Asn (leukemia cells require exogenous Asn)

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17
Q

how to reduce allergic rxn in leukemia patients treated with asparaginase?

A

put the enzyme in RBCs -> less allergic rxn

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18
Q

what aa’s can enter metabolism as pyruvate?

A

Ala
Ser
Cys

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19
Q

besides pyruvate, what is Cys also turned into?

A

taurine - bile salts

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20
Q

addition of a hydroxymethyl group to glycine forms?

A

serine

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21
Q

what intermediate can Thr be turned into that can subsequently be transformed into pyruvate?

A

aminoacetone

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22
Q

what enzyme converts Gly Ser?

A

serine hydroxymethyl transferase

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23
Q

what cofactor does serine hydroxynethyl transferase require?

A

PLP

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24
Q

ways to convert Gly -> glyoxylate

A

glyoxylate transaminase: reversible

D-aa oxidase: non-reversible

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25
what else does the Gly -> glyoxylate D-aa oxidase rxn form?
H2O2 and NH4+
26
why is glyoxylate clinically relevant?
it can form kidney stones if lacking glyoxylate transaminase = oxaluria type I
27
what is glyoxylate normally transformed into?
oxalate and alpha-hydroxy-beta-ketoadipate (requires TPP)
28
what are citrate and EDTA used for in blood collection tubes?
anti-coagulants b/c they can chelate divalent cations
29
what three aa's can be formed from 3-phosphoglycerate?
serine, cysteine, glycine
30
rxns to take 3-phosphoglycerate -> serine
1. oxidation -> 3-phosphoglycerate DH (makes NADH) 2. transamination from Glu 3. hydrolysis
31
how is Gly made from Ser?
serine hydroxymethyltransferase -> side chain methylene group of Ser transferred to TH4 to form Gly
32
how is Cys made from Ser?
1. homoCys + Ser -> cystathionine (cystathionine B-synthase) 2. cystathionine -> a-KG and Cys (deaminated, cleaved by cystathionase/cystathionine lyase)
33
where do the parts of Cys come from?
carbons from Ser | sulfur from homoCys
34
what do defects in cystathionine B-synthase cause?
homocystinuria
35
why is homocystinuria bad?
- increased risk for CHD, arteriosclerosis - dislocation of eye lens - damages cells lining blood vessels - raises oxidative stress
36
treatment for homocystinuria?
PLP (B6) - some mutations respond to this, but only if enzyme is deficient, not completely gone
37
two ways you can get homoCys accumulation?
1. defective cystathionine B-synthase | 2. defective Met synthase
38
what cofactor does cystathionine B-synthase require?
PLP
39
what cofactor does Met synthase require?
B12
40
Met synthase catalyzes what rxn?
homoCys + N5-methyl-THF -> Met + THF
41
where are most BCAA metabolized?
skeletal muscle tissue
42
what are the BCAA?
Val Ile Leu
43
[BCAA] in muscle vs. liver
higher in muscle, lower in liver
44
what does muscle use BCAA for?
used as fuel to make ATP (1 mol of BCAA = 101 mol ATP)
45
how are the amino groups dealt with in muscle after BCAA metabolism?
Ala carries the amino groups back to liver safely for disposal as urea
46
steps to BCAA metabolism
1. BCAA -> BC keto acids (BCAA transaminase) | 2. BC keto acids -> BC acyl coA (BCKA DH)
47
what is the BCKA DH rxn similar to?
pyruvate DH - requires same cofactors: - TPP - NAD+ - FAD - lipoic acid - coA
48
what cofactor does BCAA transaminase require?
PLP (B6)
49
what other byproducts does BCKA DH produce?
CO2, NADH
50
what are each of the BCAA metabolized to specifically?
Val -> propionyl coA Ile -> propionyl coA, acetyl coA Leu -> acetoacetyl coA
51
steps of propionyl coA metabolism?
1. propionyl coA -> methylmalonyl coA (carboxylase - needs bicarb, ATP, biotin) 2. methylmalonyl coA -> succinyl coA (methylmalonyl coA mutase - needs B12)
52
what deficiency is implied with a build up of methylmalonyl coA?
B12
53
why is Phe essential?
required in diet as Tyr precursor
54
why is Trp essential?
humans can't synthesize the complex heterocyclic side chain
55
how is Thr metabolized?
like BCAA
56
why is Met essential?
- provides S for Cys - methyl donor in metabolism (SAM) - homoCys recycled
57
steps for phenylalanine/tyrosine metabolism
1. Phe -> Tyr (Phe hydroxylase - needs BH4) 2. Tyr -> hydroxyphenylpyruvate (Tyr aminotransferase - needs PLP) 3. HPP -> homogentisate (HPP dioxidase) 4. homogentisate -> -> fumarate + acetoacetate (homogentisate oxidase, then fumarylacetoacetate hydrolase)
58
what disease is caused by defective Phe hydroxylase?
PKU/ hyperphenylalaninemia
59
what disease is caused by defective Tyr aminotransferase?
Tyrosinemia II
60
what disease is caused by defective HPP dioxidase?
Tyrosinemia III
61
what disease is caused by defective homogentisate oxidase?
alcaptonuria
62
what disease is caused by defective fumarylacetoacetate hydrolase?
tyrosinemia I
63
what is a less common cause of PKU?
defect in dihydropteridine reductase - enzyme needed to regenerate BH4
64
what cofactor does Phe hydroxylase need?
BH4
65
what does Phe get turned into in PKU?
phenylpyruvate
66
signs/symptoms of classic PKU
- appear normal at birth - elevated Phe in blood and urine - untreated: irreversible mental retardation, delayed psychomotor maturation, tremors, seizures, eczema, hyperactivity, mousy odor (phenylacetate)
67
how is PKU diagnosed?
mass spec
68
potential mechanisms for neurological symptoms of PKU
- competitive interaction of Phe w/ brain aa transport systems and inhibition of neurotransmitter synthesis - impaired myelin synthesis and delayed neuronal development
69
dietary restriction/supplements for PKU
- Lofenalac - avoid meat, aspartame (Asp + Phe) - diet most critical in first decade of life, but can still affect adults - Kuvan - supplements w/ large neutral aa's to compete w/ Phe
70
lofenalac
semisynthetic supplement to reduce Phe intake while maintaining normal intake of all other dietary nutrients
71
kuvan
synthetic version of BH4 - some patients respond
72
why is it important for pregnant women with PKU to be extremely careful w/ Phe levels?
high Phe affects fetal development - can cause neurological effects
73
why do PKU patients often have lighter skin and hair?
tyrosine is metabolized to dopamine and melanin - in PKU, Phe not turned to Tyr, so can't make these end products either
74
what happens in alcaptonuria?
accumulation of homogentisate -> autooxidizes -> dark, ochronotic pigment
75
what can chronic accumulation of homogentisate in cartilage cause?
ochronotic arthritis
76
what product formed in type I tyrosinemia is toxic to liver?
succinylacetate
77
symptoms of tyrosinemia I / tyrosinosis
- liver failure - cabbage odor - death w/i first year of life w/o trmt
78
treatment for tyrosinemia I
NTCB - inhibits HPP dioxygenase
79
symptoms of tyrosinemia II
- eye and skin lesions | - neurological problems
80
treatment for tyrosinemia II
-low Tyr, Phe diet
81
neonatal tyrosinemia
HPP deoxygenase activity low before birth and rises until near normal at birth - premies affected
82
what does HPP deoxygenase require
vitamin C
83
treatment for neonatal tyrosinemia
premies given a low protein diet w/ 100 mg/day of ascorbic acid
84
what does Trp degradation produce?
- formate - Ala - acetyl coA - NAD or NADP
85
what is the intermediate in Trp degradation that forms an acid excreted in urine? what is the acid?
intermediate: kynurenine acid: xanthurenic acid
86
what does kyurenine hydroxylase require?
PLP
87
what is used to test for PLP deficiency?
kynurenine hydroxylase
88
clinical relevance of xanthurenic acid?
can be a measure for tissue breakdown
89
what are Pro and His broken down to?
Glu
90
what is Ala broken down to?
pyruvate by transamination
91
what is Arg broken down to?
urea and Glu
92
what are Asp and Asn broken down to?
OAA by transamination

Biochem - Exam 2 (5 decks)

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