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a) A graph showing a large peak at alb and smaller peaks at alpha1, alpha2, beta, and gamma.  B) A photograph showing various white lines on a blue background. The top line is labeled anti-human whole serum, the next is anti-IgG, the next is anti-IgA, the next is anti-K and the next is anti-lambda. Each of these is near a band from both the normal and patient urine samples. Black arrows point to the patient’s sample next to anti-IgG and anti-k. A white arrow points to the band from the patient near anti-K.
(a) This graph shows normal measurements of serum proteins. (b) This photograph shows an immunoelectrophoresis of urine. After electrophoresis, antisera were added to the troughs and the precipitin arcs formed, illustrating the distribution of specific proteins. The skewed arcs (arrows) help to diagnose multiple myeloma. (credit a, b: modification of work by Izawa S, Akimoto T, Ikeuchi H, Kusano E, Nagata D)

Protein electrophoresis and the characterization of immunoglobulin structure

The advent of electrophoresis ultimately led to researching and understanding the structure of antibodies. When Swedish biochemist Arne Tiselius (1902–1971) published the first protein electrophoresis results in 1937, Tiselius, Arne, “Electrophoresis of Serum Globulin: Electrophoretic Analysis of Normal and Immune Sera,” Biochemical Journal 31, no. 9 (1937): 1464. he could identify the protein albumin (the smallest and most abundant serum protein) by the sharp band it produced in the gel. The other serum proteins could not be resolved in a simple protein electrophoresis, so he named the three broad bands, with many proteins in each band, alpha, beta, and gamma globulins. Two years later, American immunologist Elvin Kabat (1914–2000) traveled to Sweden to work with Tiselius using this new technique and showed that antibodies migrated as gamma globulins. Tiselius, Arne and Elvin A. Kabat. “An Electrophoretic Study of Immune Sera and Purified Antibody Preparations,” The Journal of Experimental Medicine 69, no. 1 (1939): 119-31. With this new understanding in hand, researchers soon learned that multiple myeloma, because it is a cancer of antibody-secreting cells, could be tentatively diagnosed by the presence of a large M spike in the gamma-globulin region by protein electrophoresis. Prior to this discovery, studies on immunoglobulin structure had been minimal, because of the difficulty of obtaining pure samples to study. Sera from multiple myeloma patients proved to be an excellent source of highly enriched monoclonal immunoglobulin, providing the raw material for studies over the next 20-plus years that resulted in the elucidation of the structure of immunoglobulin.

Electrophoresis showing 4 healthy patterns and 3 examples of those with myeloma. All 7 lanes contain multiple blue bands with a thick band labeled albumin. The myeloma samples have a dark band labeled gamma-globulin, while the healthy samples do not have a band here. A graph showing the total gamma-globulin amount (g/dl) in each of these samples. The healthy samples have approximately 0.1 while the myeloma samples range from 0.8 to 1.
Electrophoresis patterns of myeloma (right) and normal sera (left). The proteins have been stained; when the density of each band is quantified by densitometry, the data produce the bar graph on the right. Both gels show the expected dense band of albumin at the bottom and an abnormal spike in the gamma-globulin region. (credit: modification of work by Soodgupta D, Hurchla MA, Jiang M, Zheleznyak A, Weilbaecher KN, Anderson CJ, Tomasson MH, Shokeen M)
  • In general, what does an immunoelectrophoresis assay accomplish?

Immunoblot assay: the western blot

After performing protein gel electrophoresis, specific proteins can be identified in the gel using antibodies. This technique is known as the western blot . Following separation of proteins by PAGE, the protein antigens in the gel are transferred to and immobilized on a nitrocellulose membrane. This membrane can then be exposed to a primary antibody produced to specifically bind to the protein of interest. A second antibody equipped with a molecular beacon will then bind to the first. These secondary antibodies are coupled to another molecule such as an enzyme or a fluorophore (a molecule that fluoresces when excited by light). When using antibodies coupled to enzymes, a chromogenic substrate for the enzyme is added. This substrate is usually colorless but will develop color in the presence of the antibody. The fluorescence or substrate coloring identifies the location of the specific protein in the membrane to which the antibodies are bound ( [link] ).

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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