By Joe Luna
You likely use one everyday. For your cells, your Qiagen columns, your sucrose gradients. There’s probably a small one sitting on your bench right now, with its bigger cousin likely not much farther in a neighboring support room. You place your samples in it, it whirs and spins, and some time later you take your pellet or your supernatant without much fuss. I’m writing of course, of the centrifuge, that steady workhorse of a machine whose performance, reliability, and even physical dimensions can thankfully be taken for granted.
Today’s GOTW Theodor Svedberg (born 30 August 1884) could not afford to take his centrifuge for granted.
November 4th 1931 was a bit of a bad day for Svedberg. That morning, he had placed samples in Rotor I of his invention: the world’s first analytical ultra-centrifuge. Unlike today’s self-contained cubes, Svedberg’s machine was an oil-turbine driven monster that occupied an entire room, required oil lubrication at 800PSI, and had the rotor safely housed in a steel shell, five inches thick. Years of development with the help of private industry and the Swedish government had gone into its construction. When the centrifuge was finished in early 1931, Svedberg could say that he built a machine capable of resolving proteins. It was a technological breakthrough. The November 4th run was to be at the now routine speed of 50,000 rev/min. But upon reaching top speed, Rotor I catastrophically exploded. It seemed that years of development and heavy capital investment exploded with it.
Svedberg did not waste any grief, he immediately made plans to build Rotor II.
The fervor for such a machine in Svedberg’s mind came about from his studies in colloids: those particulate solutions of microscopic substances dispersed uniformly in another substance (think milk). Colloid chemists in the early 20th century were interested in measuring the sizes of particles dispersed in various solutions. Were they of uniform size? Or were they all of different sizes? At first glance, these seem like trivial observations, but much was riding on them, particularly when it came to understanding the properties of proteins in solution. Chemists and biologists knew very little beyond the fact that proteins were composed of amino acids, and that many proteins possessed enzymatic activities that could be measured. It was hotly debated whether a particular protein, hemoglobin say, was a complicated mix of amino acid polymers of various sizes or if it was a molecule with a simpler and uniform size. In the former camp were the colloid chemists (Svedberg included) who thought a protein would display a distribution of sizes. On the other side were early macromolecular chemists who thought that each protein’s size was sharply defined. Both were able to produce theories that would account for catalytic observations of various proteins in solution but underlying all of this were knowledge gaps that were largely technical: there were few effective ways to resolve proteins and measure their sizes (no antibodes, no HPLC, certainly no peptide synthesis). What to do?
Svedberg’s centrifuge provided part of the answer. By sedimenting a protein solution in a centrifugal field and observing the solution optically, Svedberg reasoned that size distribution measurements were possible. He outlined this idea in a 1923 paper, but the impracticalities of actually building a machine capable of producing immense centrifugal fields were a major challenge. It took eight years and a Nobel Prize for Svedberg to amass enough intellectual, political, and actual capital to build the machine. By the early 1930’s he had it, but as the explosion proved, the machine was not without problems.
Over time and further painstaking development (ie more explosions), Svedberg made remarkable observations on the sizes of proteins with the ultra-centrifuge. He focused for some time on hemocynanins, the oxygen carrying protein of horse shoe crabs (and the reason their blood is blue!). The chemist in him expected to see the protein dispersed throughout the tube indicative of different sizes of molecules, yet what he saw was the opposite: a “knife-sharp” boundary, indicating that all the molecules were the same size! And altering the pH of his solution had an interesting effect, the protein became dispersed, but at increments of whole numbers. Svedberg correctly reasoned that this meant that a macromolecule could be composed of smaller parts that were discreet in size. In the case of a pure protein, he reasoned the subunits could form a larger structure; the double leap to monomer and to multi-mer had been made.
Like the centrifuge, these are concepts that we can take for granted today and perhaps this fact outlines their significance. Svedberg is a rare biochemist to achieve scientific unit status (where 1 Svedberg=100 femtoseconds) for his pioneering work with the centrifuge and many would mark that as the ultimate immortalizing gesture: he’s the S in 80S ribosome! I prefer instead to think of his rotors. He made at least twenty-four, of which Rotors XXI and XXIV were still in daily operation for over 30 years. Now that’s scientific longevity.
1) Svedberg was a foreign Fellow of the Royal Society. The RS (being the RS) does a fantastic job of keeping track of its own, basically acting as the defacto biographer for its members in many cases. The bulk of this article was researched from: Claesson S. & Pedersen K.O. (1972) The Svedberg 1884-1971. Biographical Memoirs of Fellows of the Royal Society, 18, 594-627. doi: 10.1098/rsbm.1972.0022