CURRENT OPINION

Molecular

An interview with

  FTER WORKING on the molecular structure of simple
A substances, I had the idea back in 1934 of explain-
ing the properties of hemoglobin in terms of its molecular
structure-even though it is a very complicated molecule
of some 10,000 atoms. I had published a few papers about
it and expressed some ideas about proteins in general
`when the late Karl Landsteiner at the Rockefeller Insti-
tute for Medical Research invited me to talk with him.
He asked me how I would explain the properties of anti-
bodies in terms of their molecular structure.

My association with Landsteiner continued for two or
three years, and finally he encouraged me to publish my
ideas on the structure of antibodies and the nature of
serologic reactions. During the time that Landsteiner
gave me an education in the field of immunology, I dis-
covered that he and I were thinking about the serologic
problem in very different ways. He would ask, lV/zat do
these experiments force us to believe about the nature of
the world? I would ask, Peat is the most simple and
general picture of the world that we can formulate that
is not ruled out by these experiments? I realized that
medical and biological investigators were not attacking
their problems in the same way that theoretical physicists
do, the way I had been in the habit of doing.

Hemoglobin and Sickle Cell Anemia

What attracted my interest to the red blood cell was
an after-dinner conversation with William B. Castle of
the Harvard Medical School, in which he talked about
sickle cell anemia, the bizarre shapes of the red cells and
other features of the disease. I merely listened with inter-
est until he said that the red cells are deformed in the
venous circulation and not in the arterial, where they
resume a normal shape. I began to wonder: What accounts
for the difference? The change in pH is small. The great
difference is that on the arterial side the hemoglobin has
been oxygenated. Could it be that these patients with
sickle cell anemia form a different sort of hemoglobin
molecule from that formed by other people, molecules
that, when unoxygenated, behave like antibodies against

Linus C. Pauling, Ph.D., Nobel Laureate
Chairman, Division of Chemistry and Chemical Engineering,

California Institute of Technology, Pasadena

themselves and have the power of clamping on one to
another to form long, thin rods, which line up to form
long crystals that finally exceed the diameter of the cell
and deform it?

According to my own view of immune bodies, com-
plementary structure is responsible for the specificity of
combination between antibody and antigen. I now pos-
tulated that these hemoglobin molecules combine with
one another because of complementariness of structure:
The addition of oxygen to the molecule abolishes this, so
that it does not occur with oxyhemoglobin. If this were
so, we could explain what twisted the erythrocyte out of
shape, led to its destruction in the spleen, produced stasis
in the capillaries (because of the stickiness of the deformed
cells) and gave rise to all the other features of sickle cell
anemia-all in terms of the abnormal hemoglobin mole-
cule. It would thus be a molecular disease.

Harvey A. Itano, a physician, came to work with me
for a Ph.D. in chemistry, and I suggested that we study
this problem of distinguishing the abnormal hemoglobin
that I had postulated in sickle cell anemia. But every
experiment that he carried out, for over two years-even
using electrophoresis-gave the same results for normal
and abnormal hemoglobin, for the techniques are difficult
and the color of hemoglobin interfered. The idea, how-
ever, seemed to be so valid that we continued in spite of
the negative results. Dr. Seymour J. Singer and Dr. Ibert
C. Wells also joined in the work.

Finally, in ths third year, we came to the crucial experi-
ment. By electrophoresis at pH 6.9, we found that normal
hemoglobin moved toward the anode, while that of sickle
cell anemia moved toward the cathode,

Itano then examined the blood of parents-apparently
normal persons clinically-and found the two kinds of
hemoglobin to be present. This presented new facts in
the field of genetics.

H. E. Garrod's concept of inborn errors of metabolism
introduced the idea in 1923 that there are people with dis-
eases caused by abnormalities in their genie constitution.
As the geneticists viewed it, certain molecules were just
not manufactured at all when an abnormal, recessive,

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VOL. 6, No. 9 o MAY 1,1958


D isease

In 1949 molecular configuration was
related to a disease-in particular, sickle-
cell anemia. It thus became possible to
speak of "molecular disease." Dr. Linus
Pauling, who originated this concept,
here explains what it implies for a wide
range of the diseases of man.

allelic gene was homozygous. We showed that a defective
gene may manufacture the molecule in much the same
way as a normal gene does, except that the molecule it
produces is abnormal.

Sickle cell anemia shows up only when the patient-
the phenotype-has both genes for the disease. If he has
only one gene for it, and the corresponding gene is nor-
mal, the anemia does not manifest itself clinically, but on
the molecular level we find that he is producing both
kinds of hemoglobin in a roughly 50:50 mixture. Each
of the two genes sets up its own assembly line and begins
manufacturing hemoglobin. It is only approximately
50:50, because the efficiency of the abnormal gene is low,
and it produces only from 25 to 45 per cent of the hemo-
globin. Whatever mutation is responsible for the abnor-
mality of this gene has also interfered in some way with
its efficiency.

The lesson for geneticists is that an abnormal gene
may continue operating, giving rise to an abnormal prod-
uct, rather than simply failing to produce anything. Pre-
sumably there is also a molecular abnormality in the
gene, which is the cause of the molecular disease resident
in the hemoglobin.

Other Abnormal Hemoglobins

These studies have gone further, and it has been shown
that abnormal hemoglobins C, D, E and many others
exist. That is, there are a dozen varieties of the molecular
disease of hemoglobin. As to the degree of abnormality in
sickle cell hemoglobin, it is astonishing how small it is:
There is a discrepancy of only one-third of one per cent
in the composition of the molecule, and it involves alto-
gether only a dozen atoms. Of the 600 or so amino-acid
residues present in hemoglobin, Dr. Vernon Ingram of
the Cavendish Laboratories in England has shown that
only two are abnormal. In both of these, one amino-acid
residue of glutamic acid has been replaced by an amino-
acid residue of valine. This is the chemical pathology of
the molecular disease. Moreover, the presence of four
oxygen molecules in the 10,000 atoms of hemoglobin is

sufficient to overcome the sickling tendency of the abnor-
mal hemoglobin.

As to other molecular diseases, we should probably
have to include those hereditary disturbances in which
a gene is so abnormal that its product is entirely absent.
It is likely that in agammaglobulinemia there is a genz
defect that leads to the production of e3her very little or
no gamma globulin. Perhaps normal gamma globulin is
produced, but there is too little to do any good. Perhaps,
instead, an abnormal globulin is being manufactured and
deposited somewhere in the body, although as yet such
a thing has not been demonstrated. Similar diseases are
acatalasia, phenylketonuria and galactosemia; probably
in all these an enzyme is effectively missing, and a meta-
bolic product accumulates to the point where it becomes
toxic. In galactosemia, the enzyme galactose-l-phosphate-
transferase is not present, so that galactose accumulates
and produces mental deficiency and physical illness-
unless it can be excluded from the infant's diet in the first
place, by removing milk from the diet.

What must be learned is whether the defective gene
produces a molecule that fails to work, or a molecule with
undesirable properties (as in sickling), or no molecule at
all. When, in the general sense, all these alternatives are
considered, a disease such as atherosclerosis, with its
prominent familial character, is probably also a molecu-
lar abnormality-one in which the subject is genetically
left unable to withstand environmental stress due to the
nature of his occupation or due to certain foods which
he may take to excess. If his genes had been different, his
molecules would have been different, and theoretically
he could have withstood the adverse condition without
developing disease.

Many of the possible etiologic mechanisms of cancer
reduce to the problem of a molecular disease also. It
is likely that this is true of all diseases having a clearly
hereditary trend. Included among them is the very great
problem of mental deficiency, for, as you may know, the
curve for the distribution of the population by intelli-
gence does not follow entirely the bell-shaped curve or
Gaussian error function; rather, there is a rise at the low
end which can be accounted for by mental deficiency due
to such accidents as the inheritance of homozygous genes
for galactosemia or phenylketonuria.

I have been hesitant-perhaps not hesitant enough-
to say much about mental disease. I think that mental
deficiency is often the result of a qualitative abnormality,
and mental illness the result of a quantitative abnormal-
ity. That is, mental deficiency can result from complete
absence of certain enzymes required for bodily function,
while mental disease can be due to the presence of only
half as much of certain enzymes as may be normally
required, so that. the person is less well able to withstand
environmental difficulties. The vital chemical constitution
of a person is, I believe, one factor; environmental bur-
dens are another.                            END

PFIZER SPECTRUM

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