Serum Protein Analysis & ELISA Practical

Serum Protein Analysis

• Plasma contains 8-9% solid matter, of which proteins comprise 85%.
• Proteins in plasma are classified into albumins, fibrinogen, globulins, nucleoproteins, and conjugated proteins (e.g., lipoproteins and glycoproteins).

Protein Composition

• Albumins:
  • Represent over 50% of total plasma proteins
  • Have a lower molecular weight (average 69,000 kDa in human plasma)
  • Are more soluble
• Globulins:
  • Represent 33-45% of total plasma proteins
  • Have a higher molecular weight (average 156,000 kDa in human plasma)
  • Are subdivided into α-, β-, and γ- fractions according to electrophoresis and other techniques
• Fibrinogen:
  • Represents about 4% of plasma protein
  • Has an average molecular weight of 450,000 kDa
• Lipoproteins:
  • Are divided into high-density (α-) and low-density (β-) lipoproteins
  • Contain 35-60% protein (in α-lipoproteins) and much less protein (down to 2% in chylomicra) in β-lipoproteins

Physiological and Biochemical Importance

• Albumins:
  • Maintain osmotic pressure and blood volume
  • Are administered in hemorrhagic shock
• Plasma proteins:
  • Help maintain blood pH within narrow limits through buffering capacity
  • Play a role in transport (e.g., lipoproteins transport cholesterol esters, phospholipids, and bilirubins)
• Globulins:
  • Transport steroid hormones
  • Provide a source of amino acids to tissues and have a rapid turnover

Immunoglobulins and Antibodies

• Immunoglobulins (antibodies) are made in response to the presence of a foreign substance (antigen)
• Antibodies have specific affinity for the antigen to which they bind
• Proteins, polysaccharides, and nucleic acids are effective antigens
• Immunoglobulin G (IgG) is the major type of antibody in blood
  • Has a molecular weight of 150 kDa
  • Contains two identical sites for antigen binding