UNIVERSITY OF CALIFORNIA

SPARTMENT OF CHEMISTRY
AND CHEMICAL ENGINEERING
BERKELEY 4, CALIFORNIA

December 14, 1956

Professor Joshua Lederberg
Department of Genetics
College of Agriculture
University of Wisconsin
Madison 6, Wisconsin

Dear Professor Lederberg:

Many thanks for your letter of November 27 and the reprint which I found most
interesting. I had somehow missed this collection, I got the first oreon
"Physiology and Chemistry of Growth" but I hadn't seen this second volume and will
now get hold of the entire book, which I presume exists.

Your remarks on the necessity for bringing together these chemical autocatalytic

systems in some organized way before the SR unit will come into being adds another
aspect to the generation of the autocatalytic systems themselves, I am not at all
certain that there is anything different in kind between the evolution of an auto-
catalytic chemical system and the organization, or confluence, of two such evolutionary
sequences into a single unit, I should think that the same principles of efficiency

in chemical transformation, or what is equivalent in biological terms, "survival

value ," would select amongst random combination of these systems in exactly the sameway,

As for the discovery of chemical model systems to illustrate this, I can't draw one
forth for the asking as yet, but now that you have pinpointed what appears to you a
particular difficulty in the development of SR systems, perhaps one will come before
me in the not too distant future,

I have been visualizing the development of photosynthesis in just this way: That
is, the independent and quite separate evolution of the enzymatic systems for the
reduction of C03 using whatever reducing sources are available on the one hand, and
the also independent evolution of the porphyrin systems for the manipulation and
transfer of oxygen atoms on the other, The porphyrins here evolved not for their
light-absorbing quality but for their particular electronic structures, It happens
that such electronic structures must also absorb light in the visible region and the
random development of the ability to transfer this energy absorbed from the visible
region to chemical species led to the coupling of these two independent streams,

Now I am well aware that this is on a much higher level of organization than that
which you are seeking, but I suspect that we will be able to find relatively simple
model systems illustrating the same points,

Very truly yours,

A . ' f:
4 fay yo “ /
Mek A (as Coe

MO :nw “Melvin Calvin
Encl, Professor of Chemistry