Letter from Kai O. Pedersen to Michael Heidelberger
In this letter the physical chemist Kai Pedersen reported on experiments designed to separate and analyze antibody molecules
based on physical characteristics such as size, shape, or isoelectric point (the pH at which a molecule carries no net electrical
charge) by ultracentrifugation and electrophoresis. These experimental techniques were developed by the Nobel Prize winners
Theodor Svedberg and Arne Tiselius, respectively, at the University of Uppsala in Sweden. Heidelberger had received a Guggenheim
fellowship to spend the summer of 1934 at Uppsala in order to use ultracentrifugation to determine the size of antibodies.
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1934-11-19 (November 19, 1934)
Pedersen, Kai O.
Reproduced with permission of Lennart Pedersen.
Medical Subject Headings (MeSH):
Antigens and Antibodies: Heidelberger and The Rise of Quantitative Immunochemistry, 1928-1954
I wish to thank you and your family for all your friendliness to me and my wife here in Upsala. We are so glad of having had
the pleasure to make your acquaintance, we do hope that we some time will get the opportunity of seeing you again! And thank
you for the card from the ship, I hope you had a fine trip home in better weather than we have had here, I have never seen
so much raining here in Upsala as the last 6-8 weeks!
I regret very much that I have not written to you before, but I have had very much to do with the new method for calculating
the equilibrium runs, experimenting out the best method for determining the refractive increment in ultraviolet. I have also
been very busy with runs on the new centrifuge, first velocity runs and runs for the determination of the cell temperature
and later on equilibrium runs by 120000 r.p.m. corresponding to a centrifugal field of 550000 times gravity. In this field
it is possible to make equilibrium runs on low molecular substances, i.g. NaCl, LiC1, glycocol. I have first in the very last
time got to make the electrophoresis determinations on the hog thyro-globulin. I hope to be through with these determinations
in a week. At that time I think it will be possible to start with the calculations of the equilibrium runs with the 2 = 436
mole. I found it necessary to make equilibrium run after you depart. When I got the equilibrium runs calculated with the
new method, the values showed a rather strong drift (this was to be expected from the velocity runs, where you always had
some faster and some slower sedimentating substances than the main part). But the two equilibrium runs were both made with
the same start concentration, so there couldn't possibly be a concentration effect responsible for this. Therefore I thought
it necessary to make a new equilibrium run with two different concentrations. These gave nearly the same values for the same
distance from the axis of rotation nearly independent of what the concentration was. That means that it is no concentration
effect but that it is due to the material not being monodisperse. The main part gives a molecular weight of approximately
As soon as I get the new values calculated I shall send them to you together with all the calculations, I hope to be able
to do that within a fortnight.
Please remember me to Mrs. Heidelberger and Charlie and also to miss Tachau,
Kai O. Pedersen
P.S. Professor Svedberg has just to-day received h letter from Dr. Robert H. Hamilton of which he has asked us to send you
the enclosed copy. I don't remember, if you made any arrangements to get rid of the fat. Sometimes, f.inst. for the serum
proteins, one finds the same sedimentation constants for the fatfree as for the fat containing substances, in other cases
the fatfree substances seem to be changed quite a bit (denatured , not homogeneous). If you think of any value I should be
glad to make determination on the fatfree professor Svedberg agrees, but on the other hand it might give rise to quite a new
investigation. I have just a few days ago started dialyzing the crude extract you left for some of the next electrophoresis
experiments and for some of the experiments for the refractive increment.
[Handwritten note: Professor Svedberg is just sending an answer to Dr. Hamilton in which he refer to you.]