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Cohn Discusses Advances in Protein Chemistry at Richards Medal Award A STAFF REPORT 1 1 EW knowledge in the complex field of protein chemistry, essential to our understanding of important phenomena in biology and medicine, was discussed and demonstrated by Edwin J. Cohn at Massachusetts Institute of Technology on May 13 on the occasion of the Theodore William Richards Medal Award to Dr. Cohn by the Northeastern Section of the AMERICAN CHEMICAL SOCIETY.
In his medal address, "Interactions of Proteins and Other Body Constituenls," Dr. Cohn said that the study of such interactions could not be readily investigated until satisfactory preparations of undenatured proteins were available and until their molecular properties and their elcctrochemistry were understood. The study of such fractionations of proteins has become possible even in complex systems, at the molecular level. Huntington Hall at MIT was filled t o capacity for the medal presentation and address. As Dr. Cohn proceeded with his discussion he illustrated the various steps of protein interactions with beakers of fluids as well as with slides. Before Cohn began his address, Chester M. Alter, chairman of the Northeastern Seetion,discussed the Richards medal which has been awarded, usually biennially but more recently annually, to such eminent chemists as Noyes, Kraus, Baxter, Hudson, Keyes, Adams, and Pauling. Dr. Cohn, professor of biological chemistry and head of the department of physical chemistry at Harvard University since 1935, is the tenth scientist to b e honored with the Richards medal. Cohn's researches have been of interest and of profit to the organic chemist, Alter said, as well as to the physical chemist the physician, and the patient. The scientific work of the medalist was related by O o r g e Scat chard, department of chemistry, MIT. Before the addresses got under way, a number of members wlio could not be present at Chicago for t lie honor were awarded 50-year membership certificates by Executive Secretary Alden Emery. Following the ceremony and addresses, a reception to the medalist and distinguished guests was given in Morss Hall, MIT.
The Medal
Address
Dr. Cohn devoted part of his address to his earlier work which led to the historic and Valuable researches in blood fractions and proteins. Protein chemistry, he said, is more than a century old and has gone
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Edivin J. Cohn receives Richards medal from Chester \l. Alter of lioslon University, chairman of the ACS Northeastern Section through several phases which were described. The first must always be the separation of protein from the tissue or body fluid, and its purification from lipids, sugars, salts, and from other proteins. The gliadin of wheat was important in bread making; the casein of milk in making cheese; the fibrinogen of the blood in clotting; the hemoglobin of the red blood cell because of its color. Cohn then discussed protein colloid chemistry, and said that proteins, unlike colloids, though of large dimensions are not simple aggregates of smaller molecules but are themselves rigid molecules of a complex architecture. The polymerization of fibrinogen t o form t h e fibrin clot is not easily reversible. On t h e other hand, insulin is composed, we now believe, of three identical segments, each with a molecular weight of 12,000. Insulin dissolves in acid solution as molecules of this size, a s has been recently demonstrated by John L. Onelcy and Erie Ellcnbogcn, which reeoinbine, under the conditions in which insulin crystallizes at. neutral reactions, as a molecule three times this size with tripartite symmetry. Hemoglobin, which has a molecular weight approximating68,000, disassociates under some conditions into disks of half this weight, and it is probably for this reason that hemoglobin is readily lost from the bloodstream. Although many problems remain to be solved, regarding the internal structure of the protein, each protein must be regarded as a chemical individual with a unique arrangement of
CHEMICAL
peptide chains and of the reactive chemical groups, some are polar, some nonpolar, some charged, some uncharged, some aliphatic, some aromatic, so as to yield the spatial configurations upon which biological specificity and function depend. Dr. Cohn then reviewed the results of protein electrochemistry which began with the turn of the century and which h a s always develoixHl by the-application of laws deduced for simpler electrolytes to these inegamolocules. Sir William Hardy had noted not only that proteins moved i n an electric field but that the direction of their motion was changed with the pH of the environment. A t a particular point, therefore, a protein would not m o v e in the electric field and was said to be i n an isoelectric condition. The isoelectric point of a protein is a very characteristic property which depends on the relative number and strength of its acid and basic groups. In general, the* solubility of a protein is at a minimum at its isoelectric point. The interactions of proteins with each other also depend upon their isoelectric points since proteins c a n form salts with each other in a varioty of combining proportions. Thus the complex salt formed between insulin and a basic protein, such as globin or a protamine, is less soluble over a wide pH range than insulin. In protein fractionation, however, advantage can also be taken of the formation of less soluble protein salts in order t o extract certain proteins, but not others from a complex protein mixture. T h u s we
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have recently revised, in* stated, our system of plasma fractionation by effecting the first separation under conditions of acidity, ethanol concentration, temperature, and ionic strength such that essentially all of the albumin remains in solution, anil all of the -y-globulins in the precipitate. Si;rum 7-globulin has the most alkalincisoeleetrie point of the plasma proteins, being largely in the isoelectric si at
