Protein and Amino acid Catabolism Flashcards
(97 cards)
1
Q
Why are amino acids considered glucogenic?
A
they can be converted to OAA
2
Q
Ketogenic amino acids form what two compounds?
A
acetyl-CoA or acetoacetyl-CoA
3
Q
Which amino acids are degraded to acetyl-CoA?
A
Leucine, Isoleucine, Tryptophan
4
Q
What amino acids are degraded to pyruvate?
A
alanine, serine, cysteine , glycine
5
Q
What amino acids are degraded to oxaloacetate?
A
Aspartate and asparagine
6
Q
What amino acids are degraded to fumarate?
A
Trp, Tyr, Phe
7
Q
What amino acids are degraded to succinyl-CoA?
A
Val, Thr, Iso, Met
8
Q
What amino acids are degraded to a-KG?
A
Arg, His, Glu, Pro
9
Q
During fasting or low energy state, what enzymes activity most influences amino acid metabolism?
A
mitochondrial glutamate dehydrogenase
10
Q
What three products does glutamate dehydrogenase produce?
A
ammonium, NADH and a-KG
11
Q
What mutant enzyme do patients with HHF6 possess?
A
they express mutant forms of GDH
12
Q
What about these mutant forms of GDH predispose thee patients to hypoglycemia?
A
Their GDH is insensitive to inhibition by GTP
13
Q
What does this mutant GDH produce?
A
ATP and ammonia
14
Q
What does this excess ATP trigger?
A
insulin release
15
Q
This aberrant activity of GDH also reduces the synthesis of what? What are the effects of this?
A
N-acetylglutamate
Decreased activity of the urea cycle
16
Q
Where is oxalate secreted? What does oxalate have a high affinity for?
A
urine. Calcium.
17
Q
What is the pathway for the formation of oxalate?
A
glycine –> glyoxalate –> oxalate
18
Q
How does oxalate relate to kidney physiology?
A
calcium oxalate can precipitate and form kidney stones
19
Q
What product does the glycine cleavage system produce?
A
N5, N10 methylene THF
20
Q
Is the methylene cleavage system reversible?
A
Yes
21
Q
Defects in the glycine cleavage system lead to what?
A
glycine encephalopathy
22
Q
What is glycine encephalopathy also known as?
A
nonketotic hyperglycinemia
23
Q
What is the function of asparaginase?
A
Asparagine to aspartate
24
Q
What is the function of AST?
A
Aspartate to OAA
25
Propionyl-CoA Carboxylase requires what co-factor?
Biotin
26
Carboxylation of propionyl-CoA yields what product?
D-methylmalonyl-CoA
27
The conversion of L-methylmalonyl-CoA to Succinyl-CoA requries what co-factor?
B12
28
Where does absorption of B12 occur?
distal ileum
29
What is the function of transcobalamin?
to bind B12 once it has been absorbed
30
What is pernicious anemia?
lack of B12 (due to a number of reasons)
31
What reaction converts N5-methyl-THF back into THF? What enzyme catalyzes this reaction?
conversion of homocysteine to methionine
Methionine Synthase
32
N5, N10- methylene THF is required for the synthesis of what DNA components?
thymidine and purine rings
33
Name three tenets of how homocysteine may contribute to atherosclerosis?
oxidize LDL's
damages cells lining arteries
interference with blood clotting system
34
BCKDH is related to what other dehydrogenase?
PDH
35
What are the products of the BCAA degradation?
branched-chain acyl-CoA's
36
Oxidation of branched-chain acyl-CoA's is very similar to what other degradative pathway?
beta-oxidation
37
What is valine coverted into?
propionyl-CoA
38
What is isoleucine converted into?
propionyl-CoA and acetyl-CoA
39
What is leucine converted into?
acetyl-CoA and acetoacetyl-CoA
40
MSUD is characterized by defects in what complex?
BCKDH
41
What gives MSUD its odor?
presence of branched chain alpha-keto acids
42
What population has a high incidence of MSUD?
Old World Mennonite
43
What enzyme is defective in tyrosinemia-II?
| Tyrosinemia-II is characterized by what three conditions?
tyrosine aminotransferase
keratitis, photophobia, painful skin lesions
44
Where do these conditions of tyrosinemia-II occur?
palms of hands and soles of feet
45
What color does the urine of alkaptonuria patients turn when exposed to air? What compound provides for this? What enzyme is deficient in these patients?
black
homogentistate
Homogentistate oxidase
46
Oxidation of homogentistate produces what? What will this oxidation product cause?
benzoquinones
pigmentation (ochronosis) of connective tissue and arthritis
47
What two procedures do alkaptonuria patients often require by midlife?
joint and cardiac valve replacements
48
What is Nitisinone?
drug that impedes homogenistate formation
49
What enzyme is deficient in tyrosinemia-I?
fumarylacetoacetate hydrolase
50
What two products accumulate in patients suffering from tyrosinemia-I?
fumarylacetoacetate and maleylacetoacetate
51
In patients suffering from tyrosinemia-I, fumarylacetoacetate and maleylacetoacetate are converted to what?
succinylacetone
52
Succinylacetone can inhibit the synthesis of what?
heme
53
Which amino acids can be deaminated without the help of an aminotransferase?
serine, cysteine, histidine and theronine
54
What are the substrates of carbamoyl phosphate synthetase I?
ATP, HCO3, ammonium
55
Carbamoyl Phosphate Synthetase I requires what product as a co-factor?
n-acetylglutamate
56
What enzyme synthesizes n-acetylglutamate? What activates this enzyme?
N-acetylglutamate synthetase
arginine
57
What does carbamoyl phosphate condense with?
ornithine
58
What two steps of the urea cycle take place in the mitochondria?
formation of carbamoyl phosphate and condensation of carbamoyl phosphate with ornithine
59
What is the RLS of the urea cycle?
carbamoyl phosphate synthetase I
60
At what point does the urea cycle leave the mitochondria? How is this achieved?
citrulline is exchanged for ornithine
61
What product links the urea cycle to the citric acid cycle?
fumarate
62
What is the intestinal-renal axis?
intestinal epithelial cells produce citrulline from glutamine
renal cells pick up citrulline and convert it to arginine
63
When is the intestinal-renal axis established?
post-natally
64
Conditions affect which two organs can affect arginine synthesis?
intestine or kidneys
65
Which organ system can perform the entire urea cycle?
Liver
66
WHat are the sources of the amide nitrogen in urea?
NH4 and aspartate
67
What is the urea-TCA bicycle?
fumarate is generated by the urea cycle
OAA is converted to aspartate and utilized by the urea cycle
68
What two drugs can be used to treat patients with defects in either carbamoyl phosphate synthetase I or ornithine transcarbamoylase?
phenylbutyrate and benzoate
69
Ketogenic amino acids form what two products?
acetyl-CoA and acetoacetyl-CoA
70
Under low energy charge, what enzyme most influences amino acid degradation?
mitochondrial glutamate dehydrogenase
71
What regulates the activity of glutamate dehydrogenase?
cellular energy charge
72
Regarding the activity of GDH, what side of the equation is NADH on?
alpha-KG
73
Familial hyperinsulemic hypoglycemia have been found to possess a mutated version of what enzyme? What makes this enzyme defective?
GDH
it is resistant to inhibition by GTP
74
In HHF patients, what causes insulin secretion?
NADH acting on beta-cells
75
If now converted to serine, what else can glycine be converted to?
glyoxalate and oxalate
76
In humans, what is the major route of glycine metabolism? What does this produce?
mitochondrial glycine cleavage pathway
N5N10-methylene-THF, NADH
77
What enzyme degrades asparagine? What is the product?
asparaginase
aspartate
78
Defects in the glycine cleavage pathway lead to what?
glycine encephalopathy
AKA
nonketotic hyperglycinemia
79
What are the best sources of B12?
meats and shellfish
80
What is MSUD characterized by regarding enzymatic defects?
defective branched chain alpha-ketoacid dehydrogenase complex (BCKDH)
81
What enzyme is defective in alcaptonuriua?
homogentisate oxidase
82
What enzyme does nitisinone affect the activity of? What will this impede the formation on? What disease can this help treat?
4-hydroxyphenylpyruvate hydroxylase
homogentisate
alcaptonuria
83
What product in the urine in diagnostic of tyrosinemia-I?
succinylacetone
84
Where is carbamoylphosphate synthetase I located?
mitochondria
85
What does carbamoyl phosphate synthetase I require as an allosteric activatior?
N-acetylglutamate
86
What enzyme produces N-acetylglutamate? What product activtaes the enzyme that produces N-acetylglutamate?
N-acetylglutamate Synthetase
Arginine
87
What two enzymes of the urea cycle perform their activities in the mitochondria?
carbamoyl phosphate synthetase I and ornithine transcarbamoylase
88
What are the nitrogen sources of urea?
aspartate and ammonium
89
Infants born with defects in carbamoyl phosphate synthetase I or ornithine transbarbamoylase require the administration of what two drugs?
phenylbutyrate and benzoate
90
What two amino acids are released from the muscles in the beginning of the early fast?
alanine and glutamine
91
What is the function of tryptophan hydroxylase? What co-factor does tryptophan hydroxylase require? The activity of this enzyme leads to the formation of what?
add hydroxyl group to tryptophan
THBtn
serotonin
92
What enzyme begins the formation of melatonin? What is the enzymatic function of this enzyme? What enzyme converts N-acetylserotonin to melatonin?
N-acetyltransferase
serotonin --> N-acetylserotonin
Hydroxyindole-O-methyltransferase
93
What is GABA produced from? What co-factor does this reaction require?
glutamate
pyridoxal phosphate
94
What type of bond does GST form?
thio-ether
95
The increased degradation of glutamate to a-KG also decreases the production of what molecule involved in the urea cycle?
N-acetylglutamate
96
What enzyme of the urea cycle develops post-natally?
arginpsuccinate lyase
97
What is alpha-ketoisovalerate converted into?
ONLY glucose
