5 October 1955
Dr. Alexander Rich
Cavendish Laboratory
Cambridge
England
Dear Alex:
I am interested to learn about the structure that you and Francis Crick have formulated
for collagen. It seems to me to have serious disadvantages as compared to the one
that we have been fooling around with for three years - a smaller fraction of proline
and hydroxyproline positions actually occupied by these residues, a smaller fraction
pf possible hydrogen bonds formed, etc. - but, of course, if I had felt sure that
our structure is essentially right, we would have published a description of it some
time ago.
I note that the amide II dichroism is not very well accounted for by your structure
(if I have interpreted the structure correctly), but of course all arguments involving
infrared absorption have to be used with caution because of the real possibility of
interaction of the electric moment vectors of contiguous amide groups.
Dr. Marsh tells me that the atomic positions in leucylprolylglycine have not yet been
completely refined. The dimensions of the proline ring at present are given on the
attached sheet. The distances are probably reliable to about 0.05 A, and the angles
to about 5°. The ring seems to be nearly planar; perhaps the 7 carbon atom is flopping
through the plane, between positions about 0.2 A from the plane.
I am going to be in Washington next week, and I suppose that I shall not see you -
I don't know when you plan to get back.
You will be amused to hear that I have just seen your letter of 8 August, six weeks
after it arrived, I did not read it at once on its arrival, and covered it up with
some other papers, disinterring it only last week, when I was astounded to see that
it referred to a structure for collagen.
Sincerely yours,
Linus Pauling
