Plasma proteins

[Ref: KB2:p188]

Major class of plasma proteins

• Albumin
• Globulin
• Fibrinogen

Globulin

• Alpha-1
• Alpha-2
• Beta
• Gamma
  * Almost all gamma globulin class consists of immunoglobulins

 

Normal concentration

• Normal concentration of plasma proteins
  = 50 to 80 g/L
• Albumin
  = 45g/L
• Globulin
  = 25 g/L
• Fibrinogen
  = 3 g/L

NB:

• Immunoglobulin
  = 10 to 15g of total globulins
  * IgG = 76%
  * IgA = 16%
  * IgM = 7%
  * IgE = very low
  * [PK1:p258]

Functions of plasm proteins

• Oncotic pressure
• Transport/carrier function
• Acid-base balance
  * Buffer
  * CO2 transport
• Proteolytic systems
  * Complement system
  * Kinin system
  * Coagulation system
  * Fibrinolytic system
• Immune response
  * esp antibodies, cytokines
• Enzyme activity
  * e.g. pseudocholinesterase
• Metabolism
  * Provides amino acids for tissues for anabolic or catabolic purpose

Albumin

• Is a major component of plasma protein
  = 35-55g/L
• Net albumin synthesis
  = 12 to 15 g/day
  = 25% of daily protein synthesis by liver
• Is not a glycoprotein
  * Almost the only plasma protein that is not a glycoprotein
• Intravascular half-life in circulation
  = 20 days
• About 5% of albumin enters ISF from capillaries
  * Returns to circulation via the lymphatic system

Distribution of albumin

• Intravascular = 40 to 50%
• Extravascular = 50 to 60%

Main functions of albumin

• Oncotic pressure
• Transport/carrier function

NB:

• Can also form carbamino compound with CO2
• But quantitatively Hb is much more important

Albumin can bind to

• Free fatty acid
• Bilirubin
• Calcium
• Some hormones
  * e.g. cortisol, thyroxine
• Copper
• Drugs
  * Mostly acidic drugs
  * Basic drugs are mainly bound by alpha-1 acid glycoprotein

Structure

• 585 amino acid residues
• MW = 69000