Ultracentrifuge (Inventions)

The invention: A super-high-velocity centrifuge designed to separate colloidal or submicroscopic substances, the ultracentrifuge was used to measure the molecular weight of proteins and proved that proteins are large molecules.

The people behind the invention:

Theodor Svedberg (1884-1971), a Swedish physical chemist and
1926 Nobel laureate in chemistry Jesse W. Beams (1898-1977), an American physicist Arne Tiselius (1902-1971), a Swedish physical biochemist and
1948 Nobel laureate in chemistry

Svedberg Studies Colloids

Theodor “The” Svedberg became the principal founder of molecular biology when he invented the ultracentrifuge and used it to examine proteins in the mid-1920′s. He began to study materials called “colloids” as a Swedish chemistry student at the University of Uppsala and continued to conduct experiments with colloidal systems when he joined the faculty in 1907. A colloid is a kind of mixture in which very tiny particles of one substance are mixed uniformly with a dispersing medium (often water) and remain suspended indefinitely. These colloidal dispersions play an important role in many chemical and biological systems.
The size of the colloid particles must fall within a certain range. The force of gravity will cause them to settle if they are too large. If they are too small, the properties of the mixture change, and a solution is formed. Some examples of colloidal systems include mayonnaise, soap foam, marshmallows, the mineral opal, fog, India ink, jelly, whipped cream, butter, paint, and milk. Svedberg wondered what such different materials could have in common. His early work helped to explain why colloids remain in suspension. Later, he developed the ultracentrifuge to measure the weight of colloid particles by causing them to settle in a controlled way.


Svedberg builds an ultracentrifuge

Svedberg was a successful chemistry professor at the University of Uppsala in Sweden when he had the idea that colloids could be made to separate from suspension by means of centrifugal force. Centrifugal force is caused by circular motion and acts on matter much as gravity does. A person can feel this force by tying a ball to a rope and whirling it rapidly in a circle. The pull on the rope becomes stronger as the ball moves faster in its circular orbit. A centrifuge works the same way: It is a device that spins balanced containers of substances very rapidly.
Svedberg figured that it would take a centrifugal force thousands of times the force of gravity to cause colloid particles to settle. How fast they settle depends on their size and weight, so the ultracentri-fuge can also provide a measure of these properties. Centrifuges were already used to separate cream from whole milk and blood corpuscles from plasma, but these centrifuges were too slow to cause the separation of colloids. An uftracentrifuge—one that could spin samples much faster—was needed, and Svedberg made plans to build one.
The opportunity came in 1923, when Svedberg spent eight months as visiting professor in the chemistry department of the University of Wisconsin at Madison and worked with J. Burton Nichols, one of the six graduate students assigned to assist him. Here, Svedberg announced encouraging results with an electrically driven centri-fuge—not yet an ultracentrifuge—which attained a rotation equal to about 150 times the force of gravity. Svedberg returned to Sweden and, within a year, built a centrifuge capable of generating 7,000 times the force of gravity. He used it with Herman Rinde, a colleague at the University of Uppsala, to separate the suspended particles of colloidal gold. This was in 1924, which is generally accepted as the date of the first use of a true ultracentrifuge. From 1925 to 1926, Svedberg raised the funds to build an even more powerful ul-tracentrifuge. It would be driven by an oil turbine, a machine capable of producing more than 40,000 revolutions per minute to generate a force 100,000 times that of gravity.
Svedberg and Robin Fahraeus used the new ultracentrifuge to separate the protein hemoglobin from its colloidal suspension. Together with fats and carbohydrates, proteins are one of the most abundant organic constituents of living organisms. No protein had been isolated in pure form before Svedberg began this study, and it was uncertain whether proteins consisted of molecules of a single compound or mixtures of different substances working together in biological systems. The colloid particles of Svedberg’s previous studies separated at different rates, some settling faster than others, showing that they had different sizes and weights. Colloid particles of the protein, however, separated together. The uniform separation observed for proteins, such as hemoglobin, demonstrated for the first time that each protein consists of identical well-defined molecules. More than one hundred proteins were studied by Svedberg and his coworkers, who extended their technique to carbohydrate polymers such as cellulose and starch.

Impact

Svedberg built more and more powerful centrifuges so that smaller and smaller molecules could be studied. In 1936, he built an ul-tracentrifuge that produced a centrifugal force of more than a half-million times the force of gravity. Jesse W. Beams was an American pioneer in ultracentrifuge design. He reduced the friction of an air-driven rotor by first housing it in a vacuum, in 1934, and later by supporting it with a magnetic field.
The ultracentrifuge was a central tool for providing a modern understanding of the molecular basis of living systems, and it is employed in thousands of laboratories for a variety of purposes. It is used to analyze the purity and the molecular properties of substances containing large molecules, from the natural products of the biosciences to the synthetic polymers of chemistry. The ultracentrifuge is also employed in medicine to analyze body fluids, and it is used in biology to isolate viruses and the components of fractured cells.
Svedberg, while at Wisconsin in 1923, invented a second, very different method to separate proteins in suspension using electric currents. It is called “electrophoresis,” and it was later improved by his student, Arne Tiselius, for use in his famous study of the proteins in blood serum. The technique of electrophoresis is as widespread and important as is the ultracentrifuge.
See also Ultramicroscope; X-ray crystallography.

Next post:

Previous post: