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Clinical Chemistry 1 > Porphyrins and Hemoglobin > Flashcards

Porphyrins and Hemoglobin Flashcards

1
Q

chemical intermediates of hemoglobin, myoglobin,
cytochromes, and enzymes (catalase and peroxidase)

A

Porphyrins

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2
Q

What causes red color of hemoglobin?

A

presence of alternating double bonds of porphyrins allows the structure to absorb light

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3
Q

All porphyrins are macrocyclic structures consisting of a _________ ring linked by______ bridges.

A

tetrapyrrole, methyl

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4
Q

Porphyrins also fluoresce reddish-pink at ____ nm

A

400

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5
Q

Four ____ atoms chelate metal atoms (usually iron, competes with zinc)
▪ Iron chelates with protoporhyrin IX to form heme

A

Nitrogen

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6
Q

Iron in heme can also bind to globin proteins to form ________ &
____________.

A

HEMOGLOBIN &
MYOGLOBIN

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7
Q

fights against reactive oxygen species

A

catalase

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8
Q

hemoglobin, myoglobin, and
cytochromes all contain…

A

heme

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9
Q

Heme synthesis occurs in all cells, but primarily
____________(erythroidprecursors) and ______.

A

bone marrow, liver

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10
Q

Iron chelates with ________________ to form heme

A

protoporhyrin IX

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11
Q

Enzymes in heme synthesis localized in…

A

mitochondria and cytoplasm

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12
Q

what are the Mitochondrial enzymes involved with heme synthesis?

A

1) ALA synthase, 2) copropophyinogen oxidase, 3)
protoporhyrinoghen oxidase, and 4) ferriochelatase

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13
Q

What are the Cytoplasmic enzymes involved with heme synthesis?

A

1) ALA dehydrogenase, 2) PBG deaminase, 3)
Uroporphyrinogen III synthetase, and 4) Uroporphyrinoghen decarboxylase

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14
Q

ALA & PBG are ________soluble

A

water

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15
Q

precursors to porphyrins

A

▪ Porphyrinogens

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16
Q

these spontaneously oxidize (with light oxygen or oxidizing agents) to form three major porphyrins:

A

Porphyrinogens

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17
Q

three major porphyrins…

A
  1. Uroporphyrin [URO]: excreted in urine
  2. Coproporphyrin [CORPO]: excreted in urine and/or feces
  3. Protoporphyrin [PROTO]: excreted in feces
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18
Q

porphyrin that is excreated in urine?

A

Uroporphyrin [URO]

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19
Q

porphyrin excreted in urine and/or feces

A

Coproporphyrin [CORPO]

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20
Q

porphyrin that is excreted in feces?

A

Protoporphyrin [PROTO]

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21
Q

▪Porphyria can be inherited or caused by…

A

drugs, liver disease, anemias, or toxic
metals that cause disturbances in heme synthesis and porphyrin metabolism

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22
Q

How many enzymes are involved in heme synthesis?

A

8

Deficiency in seven of the eight enzymes involved in heme synthesis
! Leading to a distinct form of porphyria

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23
Q

Lack of enzyme activity –> decrease in formation and excretion of porphyrin or
accumulation of its __________.

A

precursors

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24
Q

Symptoms of Neurological porphyria?

A

Constipation, nausea, vomiting, severe
abdominal pain, tachycardia, hypertension,
sweating and urinary retention,

*neurotoxicity, psychiatric disturbances,
Cutaneous lesions, hyperpigmentation

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25
Q

Neurological porphyria:

Acute disturbances of porphyrin synthesis that allow accumulation of early precursors (____ and _____)

A

ALA, PBG

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26
Q

excess accumulation of all three porphyrias may cause…

A

photosensitivity, cutaneous lesions, and hyperpigmentation

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27
Q

As porphyrin molecules absorb light in
skin, electrons become excited and
eventually decay to ground state

-transferring energy to molecular oxygen
-activated oxygen species

A

Cutaneous porphyria

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28
Q

If ALA and PBG are elevated it is mostly likely what type of porphyria?

A

neurological porphyria

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29
Q

What type of porphyria causes the most skin damage?

A

protoporphyrin (not secreted in urine)

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30
Q

-Most common porphyria
-barbiturates and sulfonamides
-increased Urinary ALA, PBG, URO

A

Acute intermittent porphyria

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31
Q

Urine may turn red or black after exposure to air due to spontaneous polymerization
of PBG to porphyrin

A

Urine may turn red or black after exposure to air due to spontaneous polymerization
of PBG to porphyrin

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32
Q

NO photosensitivity with Acute intermittent porphyria, why?

A

URO won’t be accumulated in the tissue

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33
Q

Variegate porphyria is due to issues with what enzyme?

A

protopophyrinogen oxidase

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34
Q

major symptom of Variegate porphyria?

A

Photosensitivity

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35
Q

Urine: ALA URO; Feces: PROTO, COPRO

A

Variegate porphyria:

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36
Q

Photosensitivity, but less than Variegated porphyria

A

Hereditary coproporphyria

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37
Q

Urine: ALA, URO; Feces: COPRO

A

Hereditary coproporphyria

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38
Q

Porphyria cutanea tarda is due to an issue with what enzyme?

A

uroporphyrinogen decarboxylase

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39
Q

Hepatoerythropoietic porphyria

A

Porphyria cutanea tarda

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40
Q

Feces: Isocoproporphyrine, Urine:URO

A

Porphyria cutanea tarda

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41
Q

Protoporphyria is an issue with what enzyme?

A

Ferrochelatase (partial)

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42
Q

RBC, plasma, feces: PROTO, Urine: normal porphyrin
Erythropietic Protoporphyria

A

Protoporphyria

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43
Q

Congenital erythropoietic porphyria is due to an issue with what enzyme?

A

Uroporphyrinogen III synthase

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44
Q

Feces: porphyrins (Corpo, prorp), RBC, urine: increased URO I and COPRO I

A

Congenital erythropoietic porphyria

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45
Q

Erythrodontia (reddish-brown discoloring of teeth):
Disfigurement and tendency to avoid daylight

A

Erythrodontia (reddish-brown discoloring of teeth):
Disfigurement and tendency to avoid daylight

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46
Q

Unknown enzyme defect, probably coproporphyrinogen
oxidase

A

Erythropoietic coproporphyria

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47
Q

increased RBC coproporphyrin & fecal COPRO (key finding )

A

Erythropoietic coproporphyria

48
Q

acquired porphyria (secondary disorders) are a result of…

A

toxins or drugs

49
Q

How is acquired porphyria distinguished from true porphyrias?

A

only urinary ALA excretion is increased
but PBG remains normal.

50
Q

Lead poisoning inhibits….

A

inhibits ALA dehydratase and ferrochelatase

51
Q

clinically presents with increased RBC Zn-protoporphyrins and increased urinary COPRO.

A

Lead poisoning

52
Q

decreased iron in blood —-> __________ protoporphyrin

A

increased

53
Q

most common cause of increased RBC porphyrins

A

Iron deficiency

54
Q

What are the analytes in the disease of porphyrin metabolism

A

Porphobilinogen (PBG)
Urinary ALA
Fecal porphyrins
Urine porphyrins
Red cell porphyrins
Enzyme assays
Molecular genetics

55
Q

Screening method of choice for PBG is __________.

A

Watson-Schwartz

56
Q

____________ facilitates the movement of O2 from blood to muscle and serves
as a reserve O2 supply

A

Myoglobin

57
Q

Consists of a single protein chain & one heme group
▪ Located in the muscle [skeletal & cardiac]
▪ Detection method: Immunoassay

A

Myoglobin

58
Q

in general, Serum & Urine myoglobin: elevated due to…

A

Muscle damage

59
Q

Historically, it was used to monitor Severe muscle tissue damage in crush injuries
and used to aid in diagnosis and monitoring of Muscle dystrophy

A

Myoglobin

60
Q

is used to diagnose Acute MYOCARDIAL INFARCTIONS (MI)

A

Myoglobin

61
Q

myoglobin is used to detect SUCCESSFUL _____________following tPA therapy in AMI
case

A

REPERFUSION

62
Q

Can also be elevated in cases of open heart surgery, exhaustive exercise,
shock or severe renal failure

A

Myoglobin

63
Q

It is small and filters readily into the urine.
▪ Urine will turn red-dark brown.
✦ Dipstick method

A

Myoglobin in urine

64
Q

Free plasma Hb: __________ in intravascular hemolysis

A

increases

-Heart valve damage
- Complement fixation
Hb (α-chain) + Haptoglobbin
-Transported to the liver
-Cleared

65
Q

Uncleared Free plasma Hb is oxidized to…

A

metHb

66
Q

In IDA,
iron =
ferritin =
TIBC =

A

decreased
decreased
increased

67
Q

myocardial infarction:

after ____ hours, myoglobin is no longer useful. (used only for acute!)

A

24

68
Q

myocardial infarction:

What peaks at 16 hours and is back to normal in 2 days?

A

CK-MB

69
Q

myocardial infarction:

What marker is widely used for chest pain? stays elevated for a week.

A

Troponin I

70
Q

Uncleared Free plasma Hb is oxidized to _________.

A

metHb

71
Q

“methemoglobinemia”
over ____% of total Hb

A

30

72
Q

▪ At high concentrations, metHb results in…

A

hypoxia and cyanosis

73
Q

Form of Hb in which Fe2+ ! Fe3+
▪Found in oxygenated or deoxygenated form
▪ It does NOT reversibly bind to the O2

A

Methemoglobin (metHb)

74
Q

In normal individuals, ________________ will reduce Fe3+ to Fe2+
so that metHb is less than 1% of total Hb.

A

NADH metHb reductase*

  1. NADH metHb reductase
  2. Reverse NADPH metHb reductase
  3. Antioxidant Vitamins: Ascorbic acid (Vit C)
  4. **Glutathione (GSH)
75
Q

Acquired _______ in normal individuals after exposure to agents such as
nitrites, nitrates, sulfonamides, aniline dyes and pyridium.

A

MetHb

*these oxides irons exceed the body’s capacity to reduce iron

76
Q

Individuals with hereditary HbM have persistent levels of metHb which can vary. What does this lead to?

A
  1. Leading to the NADH metHb reductase deficiency 2. AA substitution in globin chain (heme pocket) Tyr ! His
77
Q

Is there hemolytic anemia with acquired MetHb?

A

NO

78
Q

How is MetHb assessed?

A

Spectrophotometry, HPLC, MS
MetHb is detected by reading absorbance at 630 nm.

79
Q

SulfHb is the result of sulfur binding to hemoglobin. Is it reversible?

A

No

80
Q

What can cause sulfhemoglobin?

A

Caused by exposure to sulfonamides or TNT in some individuals
Phenacetin, acetanilid (FDA prohibited painkiller)

81
Q

SulfHb causes apoxia and cyanosis, but rarely causes __________ formation

A

Heinz body

82
Q

CarboxyHb is the result of ______________ exposure.

A

carbon monoxide (CO)

83
Q

Complex is greatly favored and binding is reversible, but very slow.
Usually caused by exposure to automobile exhaust, industrial pollutants, tobacco smoke, etc.
Hyperbolic treatment can displace CO from hemoglobin

A

CarboxyHb is the result of carbon monoxide (CO) exposure.

84
Q

Primarily Functions of hemoglobin?

A

Transport O2 from lungs to tissues.
Acts as pH buffer

85
Q

hemoglobin is a tetramer that can carry ___ oxygens.

A

4

86
Q

what are the Four globin units?

A

2 α’s (α or ζ) and 2 β’s (ε, γ, β, or δ)

87
Q

Hb composition for adults?

A

HbA(α2 β2), HbA2 (α2 δ2)

88
Q

Fetal Hb composition?

A

HbF (α2γ2)

89
Q

Each hemoglobin composition has its unique affinity for ____

A

O2

90
Q

Embryonic hemoglobin composition?

A

Gower 1 (ζ2 ε2), Gower 2 (α2 ε2), Hb Portland (ζ2 γ2)

91
Q

What are the buffers in the body?

A

-bicarbonate
-phosphorous
-hemoglobin
-albumin (minor but still important)

92
Q

How many different hemoglobin defects are there?

A

over 700

93
Q

Hemoglobin:

Defects in structure produce a group of diseases called…

Defect in rate of synthesis or amount of α or β-globin is called…

A

hemoglobinopathies

“thalassemia”

94
Q

Structural abnormalities of hemoglobin are divided into what four groups?

A
  1. AA substitutions
    : common ones (e.g. HbM, HbS, HbC, HbD, HbE, HbO, HbG, etc)
  2. AA deletion
    (e.g. Hb GunHill)
  3. Lack of protein chain termination signal or frame shift:
    : Elongated globulin chains (e.g. Hb Constant Spring)
  4. Fused or hybrid chains (Hb Lepore or Hb Kenya)
95
Q

heptoglobin helps recycle…

A

iron

96
Q

Sickle cell mutation. Intracellular crystals of deoxygenated
HbS form causing cells to adapt a sickle shape

what mutation causes this?

A

HbS (β6 glu –> val)

97
Q

Sickle cell disease similar to HbS. Complications seem to be
less frequent than with HbS

what mutation causes this?

A

HbC (β6 glu —-> lys)

98
Q

Second most common abnormality in the world. “Thalassemictype” expression of β causes microcytic cells & normochromic anemia.

what mutation causes this?

A

HbE (β26 glu —> lys)

99
Q

No anemia, but O2 affinity is higher than normal

what mutation causes this?

A

HbD (β121glu —-> gly)

100
Q

Thalassemia of α-chains results in the tetramerization of __________________.

A

β chains

101
Q

What is Hb (Bart’s)?

A

γ4 tetramerization
Diminished α-chains synthesis: excess γ chain synthesis**

102
Q

What is HbH?

A

β4 tetramerization.
Diminished α-chain synthesis: excess β chain synthesis**

103
Q

________ is glycosylated hemoglobin
Typically due to excess carbohydrates in patients.
Useful for monitoring DM patients.

A

HbA1c***

104
Q

The elevation of GHb occurs about ___ wks after sustained elevation in blood glucose

A

3-4

105
Q

What measures how well diabetes is being managed in the last month?

A

Hemoglobin A1c

106
Q

Hemoglobin A1c:

  • Good diabetic control: ___%
  • Fair diabetic control : ____%
  • Poor diabetic control : ____%
A

7, 10, 13-20

107
Q

Hemoglobin A1c:

normal range for non DM….
pre DM range…

A

4-6

5.7-6.4

108
Q

what are the Hemoglobin Methods?

A

Electrophoresis – KNOW THESE PATTERNS***
Molecular
Chemical
HPLC
Immunological

109
Q

Electrophoresis:

Protein migration is from __________ to __________.

A

cathode (-) , anode (+)

110
Q

In the Cellulose Acetate (pH 8.4), Hbs are _________ charged

A

negatively

111
Q

In Citrate Agar (pH 6.0), some Hbs are ___________ charged

A

positively

112
Q

What is the pH for Citrate Agar and Cellulose Acetate?

A

Citrate- pH 6
Cellulose Acetate- pH 8.4

113
Q

Electrophoresis:

Where is it loaded for cellulose acetate?
Where is it loaded for citrate agar?

A

negative end

middle

114
Q

What are the methods for hemoglobin?

A

-Molecular (DNA sequencing)
-Chemical
-HPLC (Column chromatography can be used to quantify A2 in β- thalassemias)

115
Q

DNA sequencing is not useful for indicating….

A

severity of disease

116
Q

Column chromatography can be used to quantify A2 in β- thalassemias.
A2 elutes from DEAE column first, elution of other Hb’s requires higher ionic strength
buffer.
Elutes measured at 415nm and A2 is expressed as % of total Hb.

A

HPLC

Clinical Chemistry 1 (9 decks)

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