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Metabolism > Plasma proteins > Flashcards

Plasma proteins Flashcards

1
Q

What is the normal range of total plasma protein concentration?

A

6–8 g dL–1

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2
Q

How many bands are normally formed after native, non-reduced electrophoresis of blood serum?

A

5 bands (albumin, α1-globulins, α2-globulins, β-globulins, γ-globulins)

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3
Q

What are the bands formed after native, non-reduced electrophoresis of blood serum?

A
  • albumin
  • α1-globulins
  • α2-globulins
  • β-globulins
  • γ-globulins
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4
Q

Which band formed after blood serum electrophoresis is the most negatively charged?

A

Albumin

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5
Q

Which band formed after blood serum electrophoresis is the least negatively charged?

A

γ-globulins

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6
Q

How is the albumin band of blood serum electrophoresis unique compared to the other four bands?

(In terms of constituents)

A

The albumin band is formed by only protein, while the remaining 4 bands are formed of several proteins

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7
Q

What is the decreasing order of concentration of the bands of blood serum electrophoresis bands?

A

Albumin (60%) > γ-globulins (23%) > β-globulins (15%) > α2-globulins (12%) > α1-globulins (7.2%)

Values are based on the maximum normal concentration of each band and do not add up to exactly 100

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8
Q

Which of the bands of blood serum electrophoresis is most abundant?

A

Albumin

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9
Q

Which of the bands of blood serum electrophoresis is least abundant?

A

α1-globulins

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10
Q

What proteins make up the γ-globulin band?

A

Immunoglobulins/antibodies

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11
Q

What is the main constituent of the α1-globulin band?

A

α1-antitrypsin (α1-antiproteinase)

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12
Q

What are the constituents of the α1-globulin band?

A
  • α1-antitrypsin
  • α1-fetoprotein
  • α1-acid glycoprotein
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13
Q

What are the constituents of the α2-globulin band?

A
  • Ceruloplasmin
  • Haptoglobin
  • α2-macroglobulin
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14
Q

What structural feature is shared by all proteins of the α1, α2, β, and γ bands?

A

They are all globular proteins

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15
Q

What are the main constituents of the β-globulin band?

A
  • C-reactive protein (CRP)
  • Hemopexin
  • C1q
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16
Q

Where are plasma proteins synthesized?

A
  • Liver (albumin and most globulins)
  • Plasma cells, spleen, lymph nodes, bone marrow (immunoglobulins)
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17
Q

What is the major modification that most plasma proteins share?

A

Glycosylation (whether N- or O-linked), with the notable exception of albumin

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18
Q

In what form are plasma proteins synthesized?

A

As preproproteins that are cleaved, generating the active plasma protein and a signal peptide fragment

Many preproproteins are around 300 kDa in mass, while the active proteins are around 70 kDa

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19
Q

What are the main posttranslational modifications of plasma proteins?

A
  • Proteolysis (cleaving)
  • Glycosylation
  • Phosphorylation
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20
Q

What are the general functions of plasma proteins?

A
  • Nutrition (used for energy in protein malnutrition)
  • Maintenance of blood pH
  • Contributing to the viscosity of blood (especially albumin and fibrinogen)
  • Maintaining blood pressure by generating colloid–oncotic pressure (especially albumin due to its high concentration)
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21
Q

What are the specific functions of plasma proteins?

A
  • Enzymatic catalysis (e.g. thrombin, lipases)
  • Humoral immunity (immunoglobulins)
  • Blood coagulation
  • Hormonal signaling (erythropoietin stimulates erythropoiesis)
  • Transport (albumin, thyroxin-binding globulin (TBG), apolipoproteins such as LDLs)
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22
Q

By what factor do positive acute-phase proteins increase under stress conditions?

A

Up to 1000 times

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23
Q

What conditions trigger the acute-phase reactants?

A
  • Acute inflammation
  • Chronic inflammation
  • Tissue damage
  • Cancer
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24
Q

Where is albumin synthesized?

A

Liver

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25
Q

What is the shape of albumin?

A

Ellipsoid

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26
Q

How much albumin is synthesized each day?

A

12 g

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27
Q

In what form is albumin synthesized?

A

Preproalbumin

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28
Q

How is preproalbumin transformed into the albumin found in the blood?

A

preproalbumin → proalbumin + signal peptide (20–30 residues) via signal peptidase
proalbumin → albumin + hexapeptide

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29
Q

What is the structure of the mature albumin protein?

A

A single polypeptide with 3 domains and 17 disulfide bridges

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30
Q

Does albumin have a quarternary structure?

A

No, as it is formed of a single polypeptide

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31
Q

What are examples of ligands bound by albumin in the blood?

A
  • Free fatty acids
  • Bilirubin
  • Certain steroid hormones
  • Plasma Trp
  • Metals, e.g. calcium, copper, heavy metals
  • Drugs, e.g. sulfonamides, penicillin G, dicumarol, aspirin, other acidic drugs
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32
Q

What is the role of albumin in congestive heart failure?

A
  • Weak cardiac muscle leads to hypertension
  • Hypertension leads to loss of albumin at the glomeruli of the kidney
  • Lowered albumin reduced oncotic pressure, leading to increased edema
  • Increased edema leads to more hypertension
  • Continued hypertension weakens the cardiac muscle until heart failure
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33
Q

What is the diagnostic criterion for hypoalbuminemia?

A

< 2 g dL–1

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34
Q

What are the causes of hypoalbuminemia?

A
  • Cirrhosis
  • Malnutrition
  • Nephrotic syndrome
  • GI loss of proteins (e.g. in diarrhea, vomiting)
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35
Q

What is the clinical manifestation of hypoalbuminemia?

A

Edema

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36
Q

What is the cause of hyperalbuminemia?

A

Dehydration, leading to increased blood plasma volume (though the amount of albumin stays the same)

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37
Q

What is the clinical manifestation of analbuminemia?

A

Moderate edema

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38
Q

Patients with hypoalbuminemia show extreme edema, while those with analbuminemia show only moderate edema. Why is this?

A

In analbuminemia, the levels of other plasma proteins increase compensatorily, maintaining oncotic pressure

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39
Q

What is the cause of analbuminemia?

A

An autosomal recessive mutation. One of the mutations affects splicing of the albumin precursors.

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40
Q

What is the alternative name of prealbumin?

A

Transthyretin

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41
Q

What is the alternative name of transthyretin?

A

Prealbumin

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42
Q

Is prealbumin (transthyretin) the precursor of albumin?

A

No, proalbumin and preproalbumin are.
Transthyretin was called prealbumin since it moves faster than albumin in electrophoresis

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43
Q

What are the structural features of prealbumin (transthyretin)?

A
  • A small glycoprotein (0.5% carbohydrate)
  • Rich in Trp
  • 62 kDa
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44
Q

What is the half-life of prealbumin (transthyretin)?

A

About 2 days

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45
Q

How is the half-life of prealbumin useful?

A

It is short (≈ 2 days) and so acts as a sensitive indicator of disease or protein malnutrition

46
Q

What are the main functions of prealbumin (transthyretin)?

A
  • Carrier for thyroxine (T4) and triiodothyronine (T3)
  • Carrier for steroid hormones
  • Carrier for retinol
47
Q

What is the alternative name of α1-antitrypsin?

A

α1-antiproteinase

48
Q

What is α1-antiproteinase?

A

α1-antitrypsin

49
Q

What is the function of α1-antitrypsin?

A

Neutralizing trypsin and trypsin-like enzymes (e.g. elastase)

50
Q

What are the four most common alleles for α1-antitrypsin?

A
  • M
  • S
  • Z
  • F

(full notation: PiM, etc.)

51
Q

What is the most common genotype for α1-antitrypsin?

A

MM

52
Q

Which genotypes for α1-antitrypsin cause deficiency with emphysema?

A
  • ZZ
  • SZ
53
Q

Which genotypes for α1-antitrypsin cause deficiency with little clinical manifestation?

A
  • MS
  • MZ
54
Q

What is the typical clinical presentation of people with an MS genotype for α1-antitrypsin?

A

Deficiency with little clinical manifestation

55
Q

What is the typical clinical presentation of people with an MZ genotype for α1-antitrypsin?

A

Deficiency with little clinical manifestation

56
Q

What is the typical clinical presentation of people with an SZ genotype for α1-antitrypsin?

A

Deficiency accompanied by emphysema

57
Q

What is the typical clinical presentation of people with an ZZ genotype for α1-antitrypsin?

A

Deficiency accompanied by emphysema

58
Q

How can α1-antitrypsin be inactivated?

A

Oxidation of the Met358 residue

59
Q

What is the typical cause of α1-antitrypsin inactivation by oxidation of Met358?

A

Chronic lung inflammation due to smoking

60
Q

How can α1-antitrypsin contribute to liver disease?

A

The ZZ phenotype polymerizes by forming a loop with a β-sheet and aggregates in the liver
10% of cases proceed to cirrhosis

61
Q

Which genotype of α1-antitrypsin is most associated with liver disease and cirrhosis?

A

ZZ

62
Q

Where is α1-fetoprotein synthesized?

A
  • The fetal yolk sac
  • Later by the parenchyma of the liver
63
Q

What are the functions of α1-fetoprotein?

A
  • Protects the fetus from immunolytic attacks
  • Modulates the growth of the fetus
  • Transports compounds, e.g. steroids
64
Q

What condition is a low fetal/maternal α1-fetoprotein level associated with?

A

Down syndrome

65
Q

Levels of which protein can be used to screen for Down syndrome before birth?

A

α1-fetoprotein

66
Q

In what cases do levels of α1-fetoprotein increase?

A
  • Pregnancy (physiological)
  • Hepatomas (pathological)
  • Acute hepatitis (pathological)
67
Q

What is the alternative name for α1-acid glycoprotein?

A

Orosomucoid

68
Q

What is orosomucoid?

A

α1-acid glycoprotein

69
Q

What is a structural feature of α1-acid glycoprotein?

A

Highly glycosylated (41% carbohydrate)

70
Q

What are the functions of α1-acid glycoprotein?

A
  • Transports progesterone
  • Transports carbohydrates to sites of tissue injury
71
Q

In what conditions may α1-acid glycoprotein concentration increase?

A
  • Inflammation and inflammatory diseases
  • Cirrhosis
  • Malignancies
72
Q

In what conditions may α1-acid glycoprotein concentration decrease?

A
  • Malnutrition
  • Liver diseases
  • Nephrotic syndrome
73
Q

To which electrophoresis band does haptoglobin belong?

A

α2-globulins

74
Q

To which electrophoresis band does ceruloplasmin belong?

A

α2-globulins

75
Q

What are the structural features of haptoglobin?

A
  • Tetramer (two α subunits, two β subunits)
  • Glycoprotein
76
Q

How many subunits make up haptoglobin?

A

Four: two α subunits, two β subunits

77
Q

What are the phenotypes of haptoglobin?

A

Hp 1-1: α1, α1 + 2β
Hp 2-1: α1, α2 + 2β
Hp 2-2: α2, α2 +2β

78
Q

What is the function of haptoglobin?

A

Binding of free hemoglobin after hemolysis to prevent the loss of hemoglobin and iron into the urine

79
Q

What is the half-life of the haptoglobin–hemoglobin complex?

A

90 minutes, compared to 5 days for free Hp

80
Q

In what condition may levels of haptoglobin decrease?

A

Hemolytic anemia

81
Q

What are the structural features of ceruloplasmin?

A
  • Glycoprotein
  • Contains 6 atoms of copper
82
Q

To which class of proteins does ceruloplasmin belong?

(Not electrophoresis band)

A

The metallothioneins: bind to metal ions and regulate their blood levels

83
Q

What are the functions of ceruloplasmin?

A
  • Regulate the blood levels of Cu2+ (ceruloplasmin binds 90% of serum Cu2+)
  • Oxidizes Fe2+ to Fe3+ for binding by transferrin

Albumin is more important for Cu2+ transport

84
Q

In what conditions may ceruloplasmin levels decrease?

A
  • Liver diseases, especially Wilson’s disease, an autosomal recessive genetic disease
85
Q

Abnormality in levels of which plasma protein is associated with Wilson’s disease?

A

Ceruloplasmin

86
Q

Where is α2-macroglobulin synthesized?

A
  • Hepatocytes
  • Macrophages
87
Q

What is the function of α2-macroglobulin?

A
  • Inactivates proteases (e.g. thrombin) and acts as an important in vivo anticoagulant
  • Carries many growth factors
88
Q

How does nephrotic syndrome affect levels of α2-macroglobulin?

A

Levels of α2-macroglobulin increase since other proteins are lost

89
Q

Levels of which protein increase in nephrotic syndrome?

A

α2-macroglobulin

90
Q

To which electrophoresis band does C-reactive protein (CRP) belong?

A

β-globulins

91
Q

To which electrophoresis band does hemopexin belong?

A

β-globulins

92
Q

To which electrophoresis band does complement C1q belong?

A

β-globulins

93
Q

What is the function of hemopexin?

A

Binds heme formed from the breakdown of hemoglobin and other hemeproteins

94
Q

In what conditions may hemopexin levels increase?

A
  • Pregnancy
  • Diabetes mellitus
  • Malignancies
  • Duchenne muscular dystrophy
95
Q

Levels of which protein are affected by Duchenne muscular dystrophy?

A

Hemopexin

96
Q

In which conditions may hemopexin levels decrease?

A
  • Hemolytic disorders
  • Low levels at birth; the adult level is reached within the first year of life
  • Drug induced
97
Q

What is the function of CRP?

A
  • Binds a polysaccharide, fraction C in the cell wall of Staph. pneumoniae (pneumococcus)
  • Helps in the defense against bacteria and foreign substances
98
Q

How long after an incident does CRP reach its peak level?

A

48 hours

99
Q

What are the functions of complement C1q?

A
  • The first complement factor to bind an antibody
  • Triggers classical activation of the complement (decreased levels of C1q indicate circulating Ag–Ab complex)
100
Q

What is the alternative name of fibrinogen?

A

Clotting/coagulation factor I

101
Q

What are the structural features of fibrinogen?

A
  • Highly elongated, axial ratio of 20:1
  • Made up of 6 polypeptide chains, linked by disulfide bridges
  • The N-terminus is highly negative due to the presence of Glu residues. This causes its solubility and the electrostatic repulsion of plasma fibrinogen, keeping it from aggregating
102
Q

Which plasma protein transports iron?

A

Transferrin

103
Q

Which plasma proteins transport retinol (vitamin A)?

A
  • Prealbumin (transthyretin)
  • Retinol-binding protein
104
Q

Which plasma proteins transport thyroxin?

A
  • Prealbumin (transthyretin)
  • Thyroxin-binding protein
105
Q

Which plasma protein transports cortisol and corticosteroids?

A

Transcortin (cortisol-binding protein)

106
Q

What are the (positive) acute-phase proteins?

A
  • CRP
  • Ceruloplasmin
  • α1-antitrypsin
  • α1-acid glycoprotein
  • α2-macroglobulin
107
Q

What are the negative acute-phase proteins?

A
  • Albumin
  • Prealbumin (transthyretin)
  • Retinol-binding protein
  • Transferrin
108
Q

What is the diagnostic criterion for hyperproteinemia?

A

> 8 g dL–1

109
Q

What are the causes of hyperproteinemia?

A

Hemoconcentration (ratio of albumin to globulins remains constant), caused by

  • Excessive vomiting
  • Diarrhea
  • Diabetes insipidus (ADH deficiency)
  • Diuresis
  • Intestinal obstruction
110
Q

What are the causes of hypoproteinemia?

A

Conditions

  • Hemodilution (ratio of albumin to globulins remains constant)
  • Hypoalbuminemia

General causes

  • Nephrotic syndrome
  • Protein-losing enteropathy
  • Severe liver diseases
  • Malnutrition/malabsorption
  • Extensive skin burns
  • Pregnancy
  • Malignancy
111
Q

What are the causes of hypogammaglobulinemia?

A
  • Loss from the body (as with hypoproteinemia)
  • Decreased synthesis
  • Primary (genetic) immunodeficiency
  • Secondary immunodeficiency (drug induced, uremia, hematological disorders, AIDS)
112
Q

What are the causes of hypergammaglobulinemia?

A

Polyclonal
* Chronic infections
* Chronic liver diseases
* Sarcoidosis
* Autoimmune diseases
Monoclonal
* Multiple myeloma
* Macroglobulinemia
* Lymphosarcoma
* Leukemia
* Hodgkin lymphoma

Metabolism (6 decks)

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