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Medical Biochemistry > Ch. 15: Protein & a.a. Metabolism > Flashcards

Ch. 15: Protein & a.a. Metabolism Flashcards

1
Q

Why are His and Arg conditionally essential?

A

Required for optimal development & growth in infants

His essential for uremia pts (problem w/inflammation)

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2
Q

In liver dysfunction, which a.a. become essential?

A

Cys & Tyr

Cannot convert Met ➡️ Cys or Phe ➡️ Tyr

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3
Q

What is the metabolite of melamine? What problems can they cause?

A

Cyanuric acid

Form stones in kidneys ➡️ acute renal failure in infants

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4
Q

Why is it important to maintain nitrogen balance?

A

Absence of a.a. ➡️ pro synthesis stops, catabolism of unused a.a. ➡️ ⬆️ N loss in urine, ⬇️ growth

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5
Q

What is normal N balance? Negative? Positive?

A

Normal: Dietary intake of N = N loss
Negative: Dietary intake of N < N loss
Positive: Dietary intake of N > N loss

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6
Q

How are a.a. transported into cells?

A

Against concentration gradient

Semi-active process: coupled to Na+ dependent carrier system

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7
Q

What are the 5 a.a. transport systems in kidney & intestine?

A

1) Neutral
2) Acidic
3) Basic
4) Ornithine & cystine
5) Gly & Pro

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8
Q

Examples of inherited defects in a.a. transport?

A

1) Hartnup disease (neutral a.a.)
2) Cystinuria (cystine in urine)
3) Cystinosis (systemic cystine)

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9
Q

Effect of deficiency in GSH synthetase? (In gamma-glutamyl cycle for a.a. transport)

A

Accumulation of 5-oxoproline ➡️ excreted into urine ➡️ 5-oxoprolinuria

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10
Q

4 types of deamination reactions? Which is most important? Examples?

A

1) oxidative deamination (most important)
2) direct deamination: His
3) hydrolytic deamination: Asn, Gln
4) dehydrolytic deamination: Ser, Thr

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11
Q

4 examples of oxidative deamination? Which is major?

A

1) Glutamate dehydrogenase (major)
2) L-amino acid oxidase
3) D-amino acid oxidase
4) Monoamine oxidase (MAO)

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12
Q

Glutamate DH: metal ion cofactor? Requires what?

A

Zinc

NAD+ or NADP+

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13
Q

⬆️ [Glutamate DH] where?

A

Mitochondria of liver, heart, muscle, kidney

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14
Q

➕ modulators of glutamate DH?

A

ADP
GDP
some a.a.

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15
Q

➖ modulators of Glutamate DH?

A

ATP
GTP
NADH

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16
Q

Overall effect of transamination-deamination rxns depend on?

A

[substrate]

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17
Q

What is produced as by-product in transamination-deamination rxns? What happens to them?

A

1) NH3 (➡️ detoxified by: conversion to Gln & Asn or urea)
2) NADH (➡️ oxidized by ETC)

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18
Q

General steps of L-amino acid oxidase? Products?

A

Alpha a.a. ➡️ alpha-imino acid ➡️ alpha-keto acid
(Same enzyme at each step)

Alpha-keto acids, H2O2, NH4+

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19
Q

General steps of D-amino acid oxidase? Products? Where is this found?

A

Glycine ➡️ alpha-imino acid ➡️ glyoxylate
(Same enzyme each step)

Glyoxylate, H2O2, NH4+

Bacteria in gut (humans can’t have D-a.a. in body)

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20
Q

Steps of conversion from D-amino acids ➡️ L-amino acids? Enzymes?

A

D-a.a. ➡️ alpha-keto acid (D-a.a. Oxidase)

Alpha-keto acid ➡️ L-a.a. (Reamination via transaminase)

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21
Q

Norepinephrine (monoamine) ➡️ ? (via MAO)

Co-factors?

A

DOPGAL

FAD (➡️ FADH2)
H2O (➡️ NH4+)

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22
Q

2 possible products made from DOPGAL? Enzymes for each rxn?

A

1) DOPGAL ➡️ DOPEG (glycol) (aldehyde reductase)

2) DOPGAL ➡️ DOMA (acid) (aldehyde dehydrogenase)

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23
Q

General steps of dehydrolytic deamination?

Enzymes, co-factors?

A

Ser, Thr, or Homoserine ➡️ alpha-imino acid ➡️ alpha-keto acid

1) Uses specific dehydratase + pyridoxal P (H2O out)
2) NH3 out, H2O in

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24
Q

What is the most abundant a.a. in body? What synthesizes it?

A

Glutamine

Gln synthetase

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25
Main steps of glu-gln cycle? (Using glu as neurotransmitter & recycle)
Signal ➡️ gln ➡️ glu (via glutaminase) ➡️ released ➡️ recycled back to gln (via gln synthetase)
26
What co-factor is important in transamination-aminotransfer rxns? How is it bound to its apoenzyme?
Pyridoxal P Carbonyl C reacts with epsilon-amino group of lysine residue ➡️ Schiff base
27
Important transamination-aminotransfer reaction?
a.a. + alpha-KG ➡️ alpha-keto acid + glu
28
All a.a. participate in transamination rxn EXCEPT?
Lys Thr Pro OH-Pro
29
Alanine aminotransferase (ALT) same as? Substrates ➡️ products?
Glutamate pyruvate aminotransferase (GPT) Ala + alpha-KG ➡️ pyruvate + glu
30
Aspartate aminotransferase (AST) same as? Substrates ➡️ products?
Glutamate oxaloacetate aminotransferase (GOT) Asp + alpha-KG ➡️ oxaloacetate + Glu
31
Inhibitors of pyridoxal P? What do these cause?
Isonicotinic acid hydrazide Hydralazine Cycloserine Inhibit transamination
32
Role of liver in a.a. metabolism?
1) Oxidize all a.a. EXCEPT BCAAs 2) a.a. Synthesis 3) urea synthesis
33
Role of skeletal muscle in a.a. metabolism?
1) metabolize ala, asp, glu, BCAAs | 2) release ala, gln
34
Role of small intestine in a.a. metabolism?
1) metabolize dietary gln, glu, asn, asp ➡️ CO2 & H2O or lactate, ala, citrulline, NH3
35
Role of kidneys in a.a. metabolism?
1) release ser, ala 2) take up gln, pro, gly 3) acid/base regulation 4) alpha-KG ➡️ glucose or oxidized
36
Role of brain in a.a. metabolism?
1) take up BCAAs 2) glu-gln cycle 3) asp & gly = neurotransmitters 4) glu ➡️ GABA 5) tyr ➡️ dopamine, norepi, epi 6) trp ➡️ serotonin
37
How does brain use CHO, a.a., and lipids?
CHO: major fuel a.a. & lipids: for major fxns
38
NH3 toxic to brain (not other tissues) ➡️ why?
1) Hydrophobic: interferes w/membrane integrity, signal transduction 2) Depletes glu (needed as neurotransmitter) 3) Depletes TCA cycle intermediates
39
How does NH3 cause anorexia, sleep disturbances, & pain insensitivity?
⬆️ trp transport across BBB & accumulation of its metabolites (serotonin, quinolinic acid)
40
Urea synthesis: where do the 2 N come from? What is the precursor for both N?
1) free NH3 2) Asp Glu: (1) by Glu DH, (2) by AST
41
How much ATP consumed in urea synthesis?
4 ATP
42
Where is urea formed? ➡️ urine?
Made in liver ➡️ kidneys ➡️ urine
43
What is the rate-limiting step of urea synthesis in hepatocytes? Enzyme?
1st step: NH4+ + CO2 ➡️ carbamoyl P Carbamoyl P synthase I (CPS I)
44
What substrate stimulates rate-limiting step of urea cycle? How is it formed? What ➕ and ➖ this rxn?
N-acetylglutamate Acetyl-CoA + glu (via N-acetylglutamate synthase) ➕: Arg ➖: N-acetylglutamate
45
Where in hepatocyte does urea cycle take place?
Mitochondrial matrix: carbamoyl P + ornithine ➡️ citrulline Cytosol: citrulline moved out of MT ➡️ rest of cycle ➡️ ornithine moves into MT
46
Which enzyme in urea cycle is only found in liver? Fxn?
Arginase Arginine + H2O ➡️ ornithine + urea
47
CPS I: cellular location? Pathway involved? Source of nitrogen?
Mitochondria Urea cycle Ammonia
48
CPS II: cellular location? Pathway involved? Source of nitrogen?
Cytosol Pyrimidine synthesis Gamma-amide group of gln
49
3 fates of fumarate: to TCA cycle?
Fumarate ➡️ malate ➡️ MT ➡️ TCA cycle
50
3 fates of fumarate: to urea cycle?
Fumarate ➡️ malate ➡️ OAA (via malate DH) ➡️ asp ➡️ urea cycle
51
3 fates of fumarate: to glucose? (Major)
Fumarate ➡️ malate ➡️ OAA (via malate DH) ➡️ PEP ➡️ glucose
52
3 causes of hyperammonemia?
1) inborn errors of ureagenesis & organic acidemias 2) liver immaturity (transient HA of newborn) 3) liver failure (hepatic encephalopathy)
53
OCT enzyme deficiency: how is it diagnosed? What does it cause?
Allopurinol Blocks pyrimidine synthesis ➡️ Orotidinuria (⬆️ orotidine in urine)
54
Sodium benzoate: leads to? How many N lost?
Elimination of hippurate (benzoylglycine) 1 N
55
Phenylacetate or phenylbutyrate: leads to? How many N lost?
⬆️ excretion of phenylacetylglutamine 2 N
56
If NAGS enzyme deficiency, what can be given to activate CPS I?
N-carbamoylglutamate
57
What is the most common cause of hyperammonemia in adults?
Liver disease (due to ethanol abuse, infection, cancer) ➡️ ⬇️ ability to detox NH3
58
How are non-essential a.a. synthesized?
From carbon skeletons from lipid & CHO sources From transformations involving essential a.a.
59
Precursors of: glu, asp, ser, gly, tyr?
``` Alpha-ketoglutaric acid Oxalo-acetic acid 3-phospho-glyceric acid Ser Phe ```
60
Precursors of: pro, ala, cys, arg, gln, asn?
``` Glu Pyruvic acid Met & Ser Glutamate-gamma-semialdehyde Glu Asp ```
61
Arg is a precursor for which metabolites?
NO Phosphocreatine Spermine Ornithine
62
Arg ➡️ citrulline Enzyme? Co-factors?
NO synthase FMN, FAD, BH4, Fe2+, heme complex
63
How does NO cause vasodilation?
➕ modulator of guanylate cyclase (converts GTP ➡️ cGMP) cGMP ➡️ smooth muscle relaxation
64
Which a.a. is gly converted to? What type of metabolism is this?
Ser One carbon metabolism
65
Disorders of glycine metabolism: nonketotic hyperglycinemia?
Inborn error due to defect in gly cleavage enzyme complex ➡️ ⬆️ gly in body fluids (CSF)
66
Disorders of gly metabolism: ketotic hyperglycinemia?
Occurs in propionic acidemia (dysfxn of CoA metabolism ➡️ ketone bodies generated)
67
Disorders of gly metabolism: primary hyperoxaluria type I?
Deficiency of cytosolic alpha-ketoglutarate-glyoxylate carboligase ➡️ ⬆️ glyoxylate ➡️ converted to oxalate (forms crystals)
68
Creatine synthesis requires which 3 a.a.?
Arg, gly, SAM (S-adenosyl-homocysteine)
69
3 diff products obtained from Ser?
3PG Pyruvate Gly
70
Proline metabolism disorders: Ornithinemia?
Ornithine aminotransaminase deficiency
71
Proline metabolism disorders: hyperprolinemia?
Proline oxidase deficiency
72
Proline metabolism disorders: hydroxyprolinemia?
Hydroxyproline oxidase deficiency
73
Folate deficiency ➡️ accumulation of? (Synthesized from which a.a. ?) What other deficiencies cause this accumulation?
FiGlu (N-Formiminoglutamate) His Vit B12, Glu formimino-transferase deficiencies
74
Important fxn of branch-chained a.a. metabolism?
Yield high energy (amino fats)
75
What DH complex also similar to PDH and alpha-KG DH?
BCKADH (branched-chain alpha-ketoacid DH) E1 diff, E2 & E3 same
76
Products from Leu metabolism?
Acetoacetate Acetyl CoA
77
Products from Ile metabolism?
Propionyl CoA Acetyl-CoA
78
Product of Val metabolism? Requires which cofactor at which step?
Succinyl CoA Vit B12 (methylmalonyl CoA ➡️ Succinyl CoA)
79
Main fxn of SAM?
Methyl donor (in protein & cysteine synthesis)
80
Which vit needed to methylated homocysteine ➡️ methionine?
Vit B12 | Methyl donor is N5-methyl H4 folate
81
CH3 transfer rxn w/SAM ➡️ SAH acceptor: guanidinoacetic acid ➡️ ?
Creatine
82
CH3 transfer rxn w/SAM ➡️ SAH acceptor: nicotinamide ➡️ ?
N-methylnicotinamide
83
CH3 transfer rxn w/SAM ➡️ SAH acceptor: norepi ➡️ ?
Epi
84
CH3 transfer rxn w/SAM ➡️ SAH acceptor: phosphatidylethanolamine ➡️ ?
Phosphatidylcholine (3 rounds of methylation)
85
CH3 transfer rxn w/SAM ➡️ SAH acceptor: N-acetyl-serotonin ➡️ ?
Melatonin
86
How does Cys regulate its own formation?
Acts as allosteric ➖ of cysteine gamma lase (?)
87
Cys required to form which products?
Glutathione CoA-SH
88
Major end products of Cys metabolism?
Taurine: conjugated w/bile in liver ➡️ excreted by kidneys Sulfate: converted to PAPS (sulfate donor) Pyruvate
89
Abnormalities involving sulfur-containing a.a.: Hypermethioninemia: which enzyme deficient?
Met adenosyltransferase
90
Abnormalities involving sulfur-containing a.a.: Hypermethioninemia, hyperhomocysteinemia, homocystinuria: which enzyme deficient?
Cystathionine beta-synthase
91
Abnormalities involving sulfur-containing a.a.: Homocystinuria: which vitamins are deficient?
Folate | Vit B12
92
Abnormalities involving sulfur-containing a.a.: Cystathioninuria: which enzyme deficient?
Cystathionine gamma-lyase
93
Abnormalities involving sulfur-containing a.a.: Cerebral atrophy, lens dislocation: which enzyme deficient?
Hereditary sulfate oxidase
94
Abnormalities involving sulfur-containing a.a.: Cystinuria: disorder with what transport?
Renal or GI a.a. transport disorder
95
Abnormalities involving sulfur-containing a.a.: Cystinosis: which transport defective? Causes what?
ATP-dependent cystine efflux from lysosomes ➡️ cystine crystals deposited in tissues
96
Which 4 vitamins are required in homocysteine metabolism?
FH4 Vit B12 Pyridoxine Riboflavin
97
What causes hyperhomocysteinemia?
Def of enzymes in homocysteine remethylation / transsulfuration pathways
98
What are clinical manifestations of severe hyperhomocysteinemia? (Due to genetic defect in which enzyme?)
cystathionine beta-synthase Atherosclerosis, thromboembolic complications, skeletal abnormalities, ectopia lentis, mental retardation
99
Metabolism of homocysteine: steps to enter FH4 into pathway? Enzymes?
Folate ➡️ FH4 (dihydrofolate reductase, 2 NADPH) FH4 + Ser➡️ methylene FH4 + gly (ser OHmethyl transferase, vit B6) Methylene FH4 ➡️ Methyl FH4 (MTHFR) Methyl FH4 + homocysteine ➡️ met
100
What inhibits conversion of folate ➡️ FH4?
Methyltrexate
101
Steps of methylation cycle of homocysteine metabolism? Enzyme & co-factor needed in methylation of homocysteine?
Met + ATP ➡️ SAM ➡️ SAH ➡️ homocysteine + methyl FH4 ➡️ Met Methyl transferase (methylcobalamin)
102
Phe hydroxylase: where found? Requires what co-factors? What other enzyme is needed in tyr & trp hydroxylation?
Liver, kidneys BH4, NADPH Dihydropteridine reductase
103
PKU: deficiency of what enzymes/co-factors?
Phe hydroxylase, BH4, dihydropteridine reductase
104
PKU: what accumulates in urine? How is it generated? How many types of PKU are there?
Phenylpyruvate Phe ➡️ phenylpyruvate (transaminase) Types I, II, III
105
Phe ➡️ Tyr: involves BH4 ➡️ quinonoid-dihydrobiopterin Major path to regain BH4? Minor path?
Direct via Dihydropteridine reductase + NADPH With intermediate (7,8-dihydrobiopterin) via dihydrofolate reductase
106
Deficiency of what enzyme ➡️ alkaptonuria? Involved in metabolism of what a.a.? What builds up in urine ➡️ black pee
Homogentisic acid oxidase Phe, Tyr Homogentisic acid (oxidized w/air exposure)
107
Phe & Tyr are precursors for what?
T4, melanin, norepi, epi
108
Melanin is precursor to synthesize what?
Eumelanins
109
Abnormalities of tyr metabolism: Tyrosinemia type II Deficiency in which enzyme? Leads to what conditions?
Hepatic cytosolic tyr aminotransferase Hypertyrosinemia, tyrosinuria
110
Abnormalities of tyr metabolism: Tyrosinosis Deficiency of what enzyme? Leads to what conditions?
Fumarylacetoacetate hydrolase Abnormal liver fxn, renal tubular dysfxn, anemia, vit D-resistant rickets
111
Abnormalities of tyr metabolism: Albinism Cause? Some forms are from deficiency in what enzyme?
Lack of melanin production (hypomelanosis) Tyrosinase
112
Trp is involved in synthesis of what?
Nicotinic acid (amide): needed for NAD+ and NADP+ synthesis 5-hydroxytryptamine (serotonin) Melatonin Formate
113
Abnormalities of Trp metabolism: carcinoid tumor?
⬆️ serotonin synthesis
114
Abnormalities of Trp metabolism: Hartnup disease?
Disorder of renal tubular, intestinal absorption of Trp & other neutral a.a.

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