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When doctors talk about gamma globulin, or a lab separates DNA on a gel, they are using an idea Arne Tiselius made practical: charged molecules in an electric field move at different speeds. This post covers what problem he solved, what his apparatus revealed about blood, and how to calculate a protein's mobility.
Who was Arne Tiselius?
His Nobel Prize facts page says he was born on 10 August 1902 in Stockholm and died on 29 October 1971 in Uppsala. He won the 1948 Nobel Prize in Chemistry "for his research on electrophoresis and adsorption analysis, especially for his discoveries concerning the complex nature of the serum proteins".
His Nobel biography adds that after his father's early death the family moved to Gothenburg. He went to Uppsala in 1921, became an assistant in The Svedberg's laboratory in 1925, and in 1930 earned his doctorate with a thesis on the moving-boundary method for studying electrophoresis of proteins. After a year at Princeton he returned to proteins and published a much improved apparatus in 1937. He later led Uppsala's Institute of Biochemistry, was President of the International Union of Pure and Applied Chemistry from 1951 to 1955, and became President of the Nobel Foundation in 1960.
What problem did his apparatus solve?
In his Nobel lecture, Tiselius explains that the moving-boundary method was old: Oliver Lodge had used it in 1886. You fill a U-shaped tube with a protein solution under a buffer, switch on a current, and watch the boundary move.
The trouble was heat. The current warms the solution unevenly, creating density differences. When these become as large as the density differences across the boundaries, convection currents mix the liquid and destroy the boundaries.
His fix was a piece of physics you already know. Water has its maximum density at about 4 °C, so near that temperature small changes in temperature hardly change density. Running the experiment in a cold bath near 4 °C allowed a voltage gradient 8 to 10 times higher than at room temperature. He also redesigned the tube with rectangular glass cells and used schlieren optics to photograph the boundaries.
What did it reveal about blood?
The lecture describes one of the first results: serum gives several distinct components, albumin and globulins labelled with Greek letters. Later work split some of these further.
With Elvin Kabat he then asked where antibodies sit. Their 1939 paper, An electrophoretic study of immune sera and purified antibody preparations, reports that rabbit antibody is "electrophoretically identical with the γ globulin component of the serum", while horse antibody moves between the β and γ components. They also measured the isoelectric points of antibodies from several animals. That is why antibodies are often called gamma globulins. Our post on Rodney Porter and antibody structure picks up the story.
A worked example: measuring mobility
Electrophoretic mobility μ is the speed of a molecule per unit field: μ = v / E. The numbers below are sample numbers.
A boundary moves 1.8 cm in 3.0 hours in a field of 6.0 V/cm.
Time: 3.0 h = 10,800 s.
Speed: v = 1.8 ÷ 10,800 = 1.67 × 10⁻⁴ cm/s.
Mobility: μ = 1.67 × 10⁻⁴ ÷ 6.0 = 2.8 × 10⁻⁵ cm² V⁻¹ s⁻¹, which is 2.8 × 10⁻⁹ m² V⁻¹ s⁻¹.
A second protein moves 1.2 cm in the same time, so μ = 1.9 × 10⁻⁵ cm² V⁻¹ s⁻¹. After 3 hours the two boundaries are 0.6 cm apart; doubling the time doubles the gap.
Which way does a protein move? Above its isoelectric point a protein carries net negative charge and moves towards the positive electrode; below it, towards the negative one.
Common mistakes to avoid:
Forgetting to convert hours to seconds before dividing.
Mixing cm² and m² in mobility. 1 cm² = 10⁻⁴ m².
Thinking speed depends only on charge. The Nobel facts page notes molecules migrate at different speeds; the drag on each molecule matters too.
How is this different from gel electrophoresis?
Tiselius worked with proteins moving freely in liquid. Later methods run molecules through a gel, which adds sieving by size. Our guide to gel electrophoresis of DNA covers the version in your biotechnology chapter.
What can a student take from Tiselius's way of working?
Tiselius did not just repeat a known method. He found the main source of error, convection from heating, and removed it with a simple fact about water. Then he used the better tool to answer real questions about blood.
Try that in your own practicals: before taking more readings, ask what is spoiling the ones you have. If mobility, fields and charge need a refresher, the Fermi Concept Library covers every concept in physics, chemistry and biology. Tiselius trained under the inventor of the ultracentrifuge, whose story is in our post on The Svedberg and the ultracentrifuge.
Next step: redo the worked example for a field of 4.0 V/cm and check that the mobility stays the same while the distance changes.
