Porphyrins and Hemoglobin Flashcards
(92 cards)
1
Q
Hemoglobin and myoglobin are chemically similar molecules that contain what chemical groups?
A
Porphyrin groups
2
Q
Porphyrin structure
A
Cyclic structure made of 4 pyrrole rings joined by methine bridges
3
Q
What produces heme?
A
Chelation of ferrous iron to protoporphyrin
4
Q
Heme
A
Prosthetic group of Hgb responsible for binding O2
5
Q
Porphyrias
A
Group of rare disorders that result from disturbances in heme synthesis
6
Q
Hemoglobinopathies caused by
A
- Qualitative defects in Hgb (aa mutations)
- Structural defects
7
Q
Thalassemias are caused by
A
- Quantitative defects in Hgb production (less Hgb made)
- Rate and quantity made affected
8
Q
Myoglobin
A
Simple heme protein found in cardiac and skeletal muscles
9
Q
Porphyrins
A
Chem intermediates in Hgb synthesis, Mgb, and other respiratory pigments called cytochromes
10
Q
What indicates metabolic block of heme synthesis?
A
Excessive amounts of porphyrin intermediates in blood, urine, or feces
11
Q
Porphyrinogens
A
- Reduced compounds that are intermediates in heme synthesis
- Non-protein, iron-containing prosthetic group of Hgb
12
Q
How are porphyrinogens converted to porphyrins?
A
Oxidation upon air exposure
13
Q
Which of the 4 porphyrin isomers generates heme?
A
Type III isomer
14
Q
Which of the 4 porphyrin isomers occur naturally?
A
Types I and III
15
Q
Porphyrin photoactive properties (color, absorbance wavelength)
A
- Dark red color
- 400 nm
16
Q
Aqueous solubility of porphyrins varies with number of what functional group?
A
Carboxylic acid
17
Q
Number of carboxylic acid functional groups in:
Uroporphyrin
Coproporphyrin
Porphyrin
A
Uroporphyrin = 8
Coproporphyrin = 4
Porphyrin = 2
18
Q
Which cells of the human body contain hemoproteins that can synthesize heme?
A
All cells
19
Q
Primary organ sites of heme synthesis
A
Bone marrow and liver
20
Q
___ molecule(s) of heme is produced from ____ molecules of ____
A
- One
- 8
- delta-aminolevulinic acid (ALA)
21
Q
The first and last steps of heme synthesize occurs where? Requires what?
A
- Mitochondria
- Requires lots of energy
21
Q
What is the last step of heme synthesis
A
Protoporphyrin converts to heme through action of ferrochelatase adding ferrous iron
22
Q
Heme formation regulated by which mechanism? How?
A
Negative feedback whereby less heme stimulates more ALAS production
23
Q
Rate-limiting enzyme of heme synthesis
A
ALAS
24
Most heme biosynthesis disorders display what kind of inheritance pattern?
Autosomal dominant
25
Neuropsychiatric symptoms
- Abdominal pain
- Nausea
- Constipation
- Hypertension
- Psychiatric symptoms
- Fever
- Paresthesia
26
Cutaneous symptoms
- Photosensitivity
- Blisters
- Excess facial hair
- Hyperpigmentation
27
List porphyrias that feature neuropsychiatric symptoms
- ALA dehydratase deficiency porphyria (ADP)
- Acute intermittent porphyria (AIP)
28
List porphyrias that feature cutaneous symptoms
- Congenital erythropoietic porphyria (CEP)
- Porphyria cutanea tarda (PCT)
- Erythropoietic protoporphyria (EPP)
- X- linked protoporphyria (XLPP)
29
Which specific cutaneous symptoms are featured in CEP and PCT?
Increased **fragility** of light-exposed skin
30
Which specific cutaneous symptoms are featured in EPP and XLPP?
**Burning** of light-exposed skin
31
Photosensitizing effects of porphyrins attributed to what factor?
Light absorption
32
List porphyrias that feature
neurocutaneous symptoms
- Hereditary coproporphyria (HCP)
- Variegate porphyria (VP)
33
Most common acute porphyria
- Acute intermittent porphyria (AIP)
- 80% asymptomatic
34
Secondary porphyrinuria
- Acquired condition associated with increased excretion of urinary porphyrins
- Not due to inherited defect, but is rather caused by another disorder or toxin
35
Specific causes of secondary porphyrinuria
- Liver disease
- Heavy metal poisoning (Pb)
- Inherited bilirubin metabolism disorder
36
How to test for acute porphyria?
- Initial: determine if there's porphobilinogen in urine
- If positive: measure deficient PBG deaminase to ID AIP, analyze fecal porphyrins to differ btwn AIP, VP, and HCP
37
How to test for cutaneous porphyria?
- Initial: measure porphyrins in random or timed urine
- Increased excretion of porphyrins in certain pattern diagnostic for PCT and CEP
- EPP and XLPP tested using plasma or whole blood
38
List analytic methods for porphyrias
- Watson Schwartz
- HPLC with fluorescence
- Chromatographic analysis
- Fecal HPLC with fluorescence
39
Watson-Schwartz assay
Add Ehrlich's reagent to make rose red color in presence of porphyrins, absorbance 555 nm
40
Which analytical method helps to ID CEP?
Chromatographic analysis
41
Specimen requirements
- Protect from light
- Unpreserved urine must be in fridge for 48 hr or -20C for many weeks
- Fecal frozen many months -20C
- Whole blood in EDTA, protect from light, 4°C
42
Hemoglobin function
- Oxygen transport to tissue and CO2 transport back to lungs
- Major buffering system
43
Hemoglobin structure
2 alpha globins + 2 beta globins with central heme
44
Hgb A1 structure
2 alpha + 2 beta chains
45
Hgb A2 structure
2 alpha + 2 delta chains
46
Hgb F structure (fetal)
2 alpha + 2 gamma chains
47
Alpha genes on which chromosome?
- 16
- Duplicated on this chromosome (alpha 1 and 2)
48
Non-alpha genes on which chromosome?
- 11
- Non-homologous crossover -> fused/hybrid globin chains
49
Hemoglobinopathies divided into which 4 groups based on genetics of globin chain production?
1. Amino acid substitutions (Hgb S, C, D, E ,O, G)
2. Aa deletions (Hgb Gun Hill)
3. Elongated globin chains resulting from chain termination, frame shift, or other mutations (Hgb Constant Spring)
4. Fused/hybrid chains (Hgb Lepore and Kenya)
50
Which chain is affected in approx 2/3 of hemoglobinopathies?
Beta
51
Normal heme synthesis requires which 3 things?
1. Heme synthesis in mitochondria
2. Globin synthesis in cytoplasm
3. Adequate iron supply
52
Newly made heme exits the ____ to the _____ to complex with 4 globin molecules
- Mitochondria
- Cytoplasm
53
Most common hemoglobinopathy in the US, which causes sickle cell trait, and is most common in Blacks
Hgb S
54
Hgb S testing
- Solubility test
- Cellulose acetate alkaline pH Hgb electrophoresis (Hgb S between Hgb A and A2
55
Hemoglobinopathy found in West Africa-Ghana, microscopic target cells and crystalloid structures
Hgb C
56
Hgb C testing
- Cellulose acetate electrophoresis (moves with Hgb A2)
- Negative solubility test
57
Most common mixed hemoglobinopathy, microscopic target cells, occasional sickle cells, Hgb C crystal or combos
Hgb SC
58
Hgb SC testing
- Solubility test (positive)
- Cellulose acetate electrophoresis (equal amounts of Hgb S and C)
59
Hemoglobinopathy found in **Asia**, microscopic microcytosis and target cells
Hgb E
60
Hgb E testing
- Cellulose acetate
- Citrate agar (migrates with A)
61
Hemoglobinopathy with rare homozygous state usually found in Northwest India, slight anisocytosis
Hgb D
62
Hgb D testing
- Cellulose acetate (migrates with Hgb S)
- Citrate agar (migrates with Hgb A)
63
Inheritance pattern of thalassemias
Autosomal dominant
64
Thalassemia minor
- Heterozygous
- Asymptomatic
- Resembles iron deficiency
65
Thalasemia major
- Usually lethal before birth or in childhood
- Early/continuous treatment allows survival into young adulthood with many complications
66
List the 4 types of alpha thalassemias
1. Hydrops fetalis (total absence of alpha chains)
2. Hgb H (3/4 alpha chains missing)
3. Alpha-thal trait (2/4 alpha chains missing)
4. Silent carrier (1/4 alpha chains missing) -> normal Hgb production
67
Hydrops fetalis
Most clinically severe form that feature Hgb Barts and stillborn/death at birth
68
Two major subtypes of beta-thal
1. Beta+ (Beta chains made in reduced amounts)
2. Beta null (complete absence of beta chains)
69
Beta thal major
- Homozygous
- Crippling childhood disease
- Microcytic/hypochromic anemia
- BM compensates by expanding in size, thus causing bone abnormalities
70
Beta thal minor
- Heterozygous
- Inheritance of one thal gene
- RBC survival not shortened
- Asymptomatic
- Mild microcytic anemia
- Lab values resemble IDA
71
Most hemoglobinopathies and thalassemias can be diagnosed by:
- CBC
- Blood smear
- Solubility test
- Cellulose acetate electrophoresis
72
Additional tests to diagnose hemoglobinopathies and thalassemias
- Citrate agar electrophoresis
- Serum ferritin
- Newer HPLC
- Isoelectric focusing
73
Principle of solubility test
Sickled Hgb are insoluble in the deoxygenated state and thus precipitate when placed in high molarity buffer solution -> can't read lines on card thru tube
74
Solubility test false negatives
- Recent transfusion
- Infants with Hgb F anemia
75
Solubility test false positive
Whole blood vs packed RBCs
76
Does solubility test distinguish between sickle cell trait and disease?
No, so it's just a screening test, not a diagnostic test
77
Order of Hgb electrophoretic mobility from **slowest** to **fastest**
**A**ccelerated, **F**ast, **S**low, and **C**rawl
78
Universal newborn screening for ___ is now the norm
Hemoglobinopathies
79
List Hgb-based analytic methods
- Citrate agar electrophoresis
- Hgb A2 quantitation (HPLC)
- Acid elution for Hgb F
- Hgb F quantitation (HPLC)
80
Citrate agar electrophoresis
- pH 6.0-6.2
- Used **after** cellulose acetate detects abnormal Hgb
- uses solubility in determining mobility
81
Acid elution of Hgb F staining results for adult and fetal cells
Adult cells = ghost
Fetal cells = Red with eosin
82
Why use DNA technology?
Definitive diganosis of some hemoglobinopathies and thalassemias include **combos of genetic defects** that may require DNA analysis
83
DNA technology advantages
- Increased sensitivity and specificity
- Prenatal diagnosis of thal major
84
DNA technology disadvantages
Higher cost and lack of availability in routine labs
85
Myoglobin role
Reversibly binds oxygen but only releases under **low oxygen tension** from muscle membrane to muscle cell cytoplasm
86
Myoglobin structure
1 polypeptide chain + 1 heme with iron
87
How does muscle damage affect myoglobin?
Increased serum and urine Mgb
88
Which molecule features fast renal clearance and may cause acute renal failure in high concentrations?
Myoglobin
89
**T/F**
Myoglobin in urine cross-reacts with Hgb on dipstick and cause positive reaction
True
90
Myoglobin measured to test for
- rhabdomylosis
- myocardial infarction
- aid diagnosis of hereditary progressive muscular dystrophy
91
Myoglobin analytical methods
- Fluorescence
- Chemiluminescence
- Immunochromatic
