It is true that earlier investigators had observed that chlorophyll contains magnesium, besides other mineral substances. Willstätter, however, has the merit of having been the first to recognize and to prove with complete evidence the fact that magnesium is not an impurity, but is an integral part of the native, pure chlorophyll - a fact of high importance from the biological point of view. He has shown that magnesium is held within the chlorophyll molecule in a manner which is very similar to the way in which iron is held in haemoglobin; this bond is so firm that the magnesium is not liberated even by the action of a strong alkali. On the other hand, it can be removed by an acid without injury to the remainder of the chlorophyll molecule, and the magnesium-free chlorophyll which can be obtained in this way is well suited to certain investigations. Willstätter has made use of this circumstance to test to what extent chlorophyll can be the same in different kinds of plants.
Richard Martin Willstätter
Nobelprize in chemistry
1915, Munich University, Gemany. b 1872, d. 1942
Investigations carried out on more than 200 different plants, both phanerogamia and cryptogamia, showed that the chlorophyll was the same in all the kinds so far examined. This chlorophyll is, nevertheless, not a chemically homogeneous substance. It is a mixture of two somewhat different but yet closely related chlorophylls, one of them being blue-green, the other yellowgreen, and the former occurring more richly in the leaves than the latter.
During the last few years Svedberg has completed an extremely ingenious invention, the so-called ultracentrifuge, which enables highly interesting investigations to be made also on such molecular-disperse systems. We know that when a slurry, an emulsion, is put into a rapidly rotating motion, its heavier constituents are thrown outwards in the direction of the periphery of the motion. This happens in the most used of all centrifuges, the milk separator, where the skimmed milk is pressed outwards whilst the lighter fat particles, the cream, accumulate inwards and can therefore be separated. Similarly in a solution, when centrifuging is sufficiently rapid, the molecules of the dissolved substance must accumulate outwards if they are considerably heavier than the molecules of the solvent. After overcoming exceptional experimental difficulties Svedberg succeeded in demonstrating this with the aid of an apparatus which allows the enormous speed of rotation of 40,000 revolutions per minute, and in which through a highly refined arrangement the progressive distribution of the particles within the extremely rapidly whirling solution can be observed and recorded photographically.
The Svedberg, Uppsala University, Sweden. Nobelprize in chemistry
1926. b. 1884, d. 1971.
Nobel Prize in Chemistry 1946. James Batcheller Sumner (b. 1887,d. 1955), Cornell University, Ithaca, NY, USA, John Howard Northrop (b. 1891, d. 1987) & Wendell Meredith Stanley (b. 1904, d. 1971), Rockefeller Institute for Medical Research, Princeton, NJ, USA.
...The important question of the nature of the enzymes remained unsolved, however, in spite of the energetic efforts of the research workers. It is manifestly a question of substances of complicated structures, which are present in such extremely small amounts that they, so to speak, slip through the fingers when one tries to grasp them...
...In 1926, however, in connection with his studies of a special enzyme "urease", James B. Sumner of Cornell University, Ithaca, U.S.A. succeeded in producing crystals which exhibited strikingly great activity. The basic material was the bean of a South American plant, Canavalia ensiformis, in America called the "jack bean", and the crystals had an activity that was about 700 times as great as that of bean flour. What was still more important was that it was possible to dissolve the substance and re-crystallize it several times without its activity being affected. The crystals proved to consist of a protein substance. Sumner expressed the opinion that in reality this protein substance was the pure enzyme.
...Sumner's pioneer work was not immediately followed by similar work in other quarters, which might perhaps have been expected. About three years after Sumner's work had been published, however, Dr John Northrop of the Rockefeller Institute at Princeton began to work on the purification of the protein-splitting enzymes met with in the digestive apparatus and gradually succeeded in obtaining a number of them in crystallized form, e.g. the pepsin met with in the gastric juice and the trypsin and chymotrypsin in the pancreas. Northrop and his collaborators, among whom should be mentioned in the first place Kunitz, also made extremely comprehensive studies of the homogeneity and purity of these purified enzymes, and in that connection gave further proof of their nature as protein substances.
This year's third Nobel Prize winner in Chemistry, Dr Wendell Stanley, first worked at the Rockefeller Institute in New York but moved in 1932 to the department of that Institute at Princeton. The problem which attracted his attention, namely the chemical nature of the viruses, was to a certain degree analogous to the problem of the enzyme just mentioned. As is well known, viruses are contagia which give rise to a large number of the best known illnesses in man, animals and plants, e.g. smallpox, infantile paralysis, influenza, foot-and-mouth disease, mosaic disease (on tobacco plants), etc. The virus particles are invisible in the microscope, and when Stanley began his work, they could only be identified by the symptoms of disease which they occasioned. Thus the problem was more difficult, inasmuch as the effect of the virus could not be as easily measured as that of an enzyme, where an exactly known chemical reaction can be employed. Stanley first tried to show the protein nature of viruses by studying how the virus of the tobacco mosaic disease was attacked by protein-splitting enzymes, but in 1934 he passed on to attempting to purify that virus by methods similar to those which Sumner and Northrop had employed so successfully for enzymes. In 1945, by using large quantities of infected tobacco leaves, he did succeed in producing small amounts of crystals which were extremely active, and which, after detailed investigation, proved to be the bearers of the virus's activity. Here, too, it was a matter of active protein substances. Subsequently it has been proved that nucleic acid also forms an important constituent of the latter.