Presentation Speech by Professor Bo G. Malmström of the Royal Swedish Academy of Sciences

Translation from the Swedish text

Your Majesties, Your Royal Highnesses, Ladies and Gentlemen,

In the beginning there was light. Light played an important role in the origin of life on earth, and the radiation of the sun is an absolute prerequisite for the forms of life which today inhabit our planet. In the green leaves of plants solar light is converted to chemical energy, which is used as nutrition not only by the green plants themselves but also, for example, by cows who eat green grass, by ourselves who eat the meat of the cow and drink its milk, and so on through the nutritional chain.

The energy required for life processes is to a large extent liberated in the combustion of sugar and fat by the oxygen of the air. This process can, however, continue indefinitely thanks to the fact only that the nutritional substances used up are re-manufactured in the photosynthesis of green plants. In photosynthesis the plants use solar energy to build up complicated nutritional substances from two simple molecules, carbon dioxide and water, with concomitant liberation of oxygen. In the respiration in the cells of living organisms this nutrition is then reconverted to carbon dioxide and water, so that there is a continuous cyclic process driven by the sun.

In respiration as well as in photosynthesis, electrons fall from a higher to a lower energy level, somewhat like an electric current. They do not, however, pass through an electric wire but are transferred between a number of complicated proteins, which often contain metals, e. g. iron. The principles of electron transfer between simple metal compounds has been analyzed in detail by Henry Taube, the Nobel Prize winner for chemistry in 1983. An important goal in the chemical research of today is to extend these contributions in order to explain the more complicated biochemical processes.

The proteins mediating the electron transfer are organized in large molecular aggregates which are bound to biological membranes. In the electron transfer energy is liberated, and this is used to make ATP, the universal energy storage molecule of living cells. The ATP formation takes place according to a mechanism formulated by the Nobel Prize winner for chemistry in 1978, Peter Mitchell.

For a long time it has been impossible to prepare membrane-bound proteins in a form allowing the determination of the detailed structure in three dimensions. Before 1984, there were only rather fuzzy structural pictures available for a few membrane proteins. These had been derived with the aid of an electron microscopic method developed by the Englishman Aaron Klug, who was awarded the Nobel Prize in chemistry in 1982 for this achievement. But the situation had actually drastically changed in 1982, when Hartmut Michel thanks to systematic experiments succeeded in preparing highly ordered crystals of a photosynthetic reaction center from a bacterium. With these crystals he could in the period 1982-1985, in collaboration with Johann Deisenhofer and Robert Huber, determine the structure of the reaction center in atomic detail.

The structural determination awarded has led to a giant leap in our understanding of fundamental reactions in photosynthesis, the most important chemical reaction in the biosphere of our earth. But it has also consequences far outside the field of photosynthesis research. Not only photosynthesis and respiration are associated with membrane-bound proteins but also many other central biological functions, e. g. the transport of nutrients into cells, hormone action or nerve impulses. Proteins participating in these processes must span biological membranes, and the structure of the reaction center has delineated the structural principles for such proteins. Michel’s methodological contribution has, in addition, the consequence that there is now hope that we can determine detailed structures also for many other membrane proteins. Not least important is the fact that the reaction center structure has given theoretical chemists an indispensable tool in their efforts to understand how biologic electron transfer over very large distances on a molecular scale can occur as rapidly as in one billionth (American English, trillionth) of a second. In a longer perspective it is possible that such research can lead to important energy technology in the form of artificial photosynthesis.

Drs. Deisenhofer, Huber and Michel,

I have tried to describe – in Swedish – how your determination of the structure of a photosynthetic reaction center has lead to a leap in our understanding of the perhaps most important chemical reaction on earth. But it has also major implications far outside the field of photosynthesis by clarifying the structural principles for membrane proteins and by providing theoretical chemists with an important tool for understanding the basis of rapid electron transfer in biological systems. It is for these fundamental contributions that the Royal Swedish Academy of Sciences has decided to award to you this year’s Nobel Prize in chemistry.

On behalf of the Academy I wish to convey to you our warmest congratulations, and I now ask you to receive the Prize from the hands of His Majesty the King.