CHEM-342 INTRODUCTION TO BIOCHEMISTRY

Background and Assignments for the article by L. Pauling, H. A. Itano, S. J. Singer, and I. C. Wells (1949) Sickle Cell Anemia, A Molecular Disease, Science 110, 543 - 548.

Background

With the benefit of hindsight, we can pick out observations that, if properly interpreted, would have suggested the genetic relationship between sickle-cell anemia and sickle-cell trait, and a functional relationship between hemoglobin and the sickle cell trait. Diggs et al. (1), for example, noted in 1933 that the proportion of sickled erythrocytes was greater in people with anemia than in people with the trait. They also noted that sickling was time-dependent under a sealed cover slip. From those observations one might have deduced a genetic relationship and the idea that oxygen consumption (equate with hemoglobin deoxygenation) promoted sickling. However, at that time the idea of "one gene, one protein" had not been conceptualized and biochemists knew very little about the chemical nature of proteins (2,3).

Linus Pauling (4), perhaps the most impressive scientist of the 20th century, made the connection, formulated a hypothesis, tested it, and described the results in the article you are about to read. Why would Pauling, a chemist who received two unshared Nobel Prizes, be the person to make the discovery of hemoglobin S, arguably a discovery worthy of another Nobel Prize?

Although Pauling gained stature for his monumental work on the nature of chemical bonds, he had an interest in the chemistry of hemoglobin. In the 1930's he proposed a new structural and mathematical model for cooperative binding of oxygen by hemoglobin (5). He demonstrated that the spectral changes in hemoglobin, attributed to oxidation and reduction of hemoglobin by Stokes (6), were due to the change in electronic spin states of heme iron when liganded to molecular oxygen (7). In 1951 on theoretical grounds, he proposed the -helix (8), a regular structure assumed by 70% of the polypeptide chain in hemoglobin. Given Pauling's familiarity with hemoglobin, his deduction that the sickling of red blood cells which occurred at low oxygen tension must be due to a hemoglobin with distinct properties seems almost obvious in retrospect. What is surprising is that no one before Pauling made the same deduction. Shortly before his death in 1994, Pauling described the flash of insight which came to him almost half a century before (9).

.....Bill Castle, a physician from Peter Bent Brigham Hospital and Children's Hospital in Boston, talked about sickle cell anemia. I was not especially interested in what he was saying, because at that time I felt that diseases were just too complicated for me to attempt to understand. He mentioned that the red blood cells were twisted out of shape in the blood of patients with this disease. I thought to myself, there are probably thousands of different chemical substances in the red blood cell, and I don't think I can understand why a cell would be twisted out of shape. Then, went on to explain that they twisted out of shape in venous blood, but resume their normal flattened spherical shape in arterial blood. Within a few seconds the idea flashed through my mind that red cells contain a great amount of hemoglobin - about one-seventh of the content of a cell is hemoglobin molecules - and that difference between venous blood and arterial blood is that in venous blood the hemoglobin is present as hemoglobin itself, whereas in arterial blood it becomes oxyhemoglobin because there are oxygen molecules attached to the iron atoms. .... It immediately occurred to me that sickle-cell anemia must be a disease of the hemoglobin molecule, with sickle-cell hemoglobin having an abnormal structure...(9).

This was in March 1945. The deduction was a hypothesis that needed to be tested. Pauling immediately began assembling a group of research workers who could attack the problem. Harvey Itano, with a B.S. in Chemistry from the University of California and an M.D. from St. Louis University, joined Pauling's group to work on a Ph.D. Jon singer, a postdoctoral fellow, helped out. Work proceeded slowly. The article describing their work appeared in late November 1949, almost five years after Pauling's original insight. Of all the scientific articles you will read this semester, this is the probably the most clearly written. Note how exquisitely the ideas flow in logical order in the introduction. Also note that even Pauling made mistakes. See if you can recognize the incorrect reference.

References

  1. * Diggs, L. W., Ahmann, G. F., and Bibb, J. (1933) The incidence and significance of the sickle-cell trait, Ann. Internal Med. 7, 767 - 778.
  2. Edsall, J. T. (1979) The development of the physical chemistry of proteins, 1898 -1940, Ann. N.Y. Acad. Sci. 325, 53 - 74.
  3. Fruton, J. (1972) Molecules and Life - Historical Essays on the Interplay of Chemistry and Biology. Wiley-Interscience, New York.
  4. Zewail, A. (ed) (1992) The Chemical Bond: Structure and Dynamics. Academic Press, New York. (This collection of articles, mostly by Nobel Prize winners, honor Linus Pauling on his 90th birthday.)
  5. Pauling, L. (1935) The oxygen equilibrium of hemoglobin and its structural interpretation, Proc. Natl. Acad. Sci. USA 21, 186 - 191.
  6. * Stokes, G. G. (1864) On the reduction and oxidation of the colouring matter of blood, Proc. Royal Soc. London 13 355 - 364.
  7. Pauling, L. and Coryell, C. D. (1936) The magnetic properties and structure of hemoglobin, oxyhemoglobin and carbonmonoxyhemoglobin, Proc. Natl. Acad. Sci. USA 22, 210 - 216. (Magnetic Resonance Imaging (MRI) of brain activity detects specific parts of the brain that are performing tasks by their oxygen uptake. This is revealed by the sudden and local formation of deoxyhemoglobin with its distictive magnetic properties. See Scientific American, 270(April) 58 - 64 (1994).)
  8. Pauling, L., Corey, R. B., and Branson, H. R. (1951) The structure of proteins: Two hydrogen-bonded helical configurations of the polypeptide chain, Proc. Natl. Acad. Sci. USA 37, 205 - 211.
  9. Pauling, L. (1993) The Forward to Sickle Cell Disease: Basic Princilpes and Clinical Practice, pp. xvii - xix, (S. H. Embury, R. P. Hebbel, N. Mohandas, and M. H. Steinberg, eds), Raven Press, New York.

* References included in the course reader.

Assignments

Period 1, Personal and Group Learning Issues: Groups pursue personal and group learning issues. Be sure to resolve issues related to electrophoresis before next period.

Period 2, Demonstration of Electrophoresis: Lecture demonstration of the electrophoretic separation of hemoglobin variants.

Period 3, Abstracts and Future Research: Resolve any remaining learning issues. Discuss what a biochemist would do next. Individual abstracts of the Pauling et al. article are due at the beginning of class.

Period 4, Pauling Video: A video on Linus Pauling's life will be shown.

C342/S95 HBW


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Last updated Feb. 24, 1997.
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