May 12, 1952
Professor A. R. Todd, F.R.S.
University Chemical Laboratory
I am glad to have your letter of 6th May. Ava Helen and I are still feeling very
disappointed that we could not have our visit in England. I must say that I am astounded
that the State Department should have refused me a passport, after I had pointed out
clearly that the visit to England was to be purely for scientific purposes - especially
since the principal reason for the trip was to take part in the Royal Society discussion
meeting. We hope that the present situation will not continue into the future, and
that we shall be able at some future time to visit you.
I am pleased to have you say that you will not allow your new government job to cripple
your scientific work (I do not think that you should call it your ordinary scientific
work - it seems to me to be extraordinary).
We are only rather slowly beginning work in the field of nucleic adds and nucleoproteins,
but I hope that in another year or two the work on ordinary proteins will have progressed
so far as to justify our turning our attrition largely to nucleoproteins. Will you
send me reprints of your papers on nucleic acids, especially those in which you discuss
your new ideas about the bonding?
Corey is now in England, and I hope that you will talk with him. I do not know what
part of this month he plans to spend in Cambridge, but I think it very likely that
he will come to see you.
Right now we are working hard on the structure of silk fibroin. We have found a structure
that, so far as the calculations have gone yet, accounts essentially perfectly for
the observed intensities of x—ray diffraction. If the remaining calculations give
as good results, we shall have, for the first time in the history of proteins, a protein
structure which has been tested by completely detailed comparison of observed and
calculated x-ray intensities. Our structure involves alternation of glycine residues
and other residues, principally alanine; we have not taken into consideration the
side-chain atoms other than the β-carbon atoms.
There is a faint superstructure, which seems to be due in the main to the presence
of occasional serine residues - perhaps every sixth residue in each polypeptide chain
is a serine residue. However, it seems unlikely that the structural basis of the
superstructure, involving these rarer amino acid residues, can be determined without
a great deal more work.
I enclose a copy of a statement that I made about my passport, a letter that I sent
to President Truman, in an effort to get the original decision changed, and a statement
about my political beliefs that I made last year.
With best regards, also to Alison and the children, I am