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ATP synthase (Molecule of the Month for November 1997)

Chemistry Nobel Prize 1997



This year's Nobel prize for Chemistry has been awarded to Dr John Walker, Dr Paul Boyer and Dr Jens Skou. Dr John Walker, who is currently a senior scientist at the Medical Research Council Laboratory of Molecular Biology in Cambridge. Dr Walker studied for his BA at St Catherine's College, Oxford, and was awarded a D.Phil. in 1969.

The award is for Dr John Walker's study of the enzymes involved in the production of adenosine triphosphate, which acts as a store of energy in bodies called mitochondria inside cells. The results have helped to confirm a model, proposed by Dr Boyer, for the formation of ATP from adenosine diphosphate and inorganic phosphate, by the unusual spinning action of an enzyme that helps to extract energy from food.

Beginning in the 1950s, Boyer invented a range of chemical techniques for probing enzyme behaviour from which he inferred how ATP synthase works. In 1994, Walker showed that Boyer's model was correct by uncovering the enzyme's three-dimensional shape, using X-ray crystallography. "Making the crystal was the key step," says Walker. "It took about seven years." David Eisenberg, a molecular biologist and colleague of Boyer's at UCLA, says: "Boyer's inferences were confirmed in astonishing detail by a brilliant and difficult crystal structure."

The energy released when cells break down molecules of fat and carbohydrates is used to create an excess of protons on one side of a membrane. Using ATP synthase, cells harness this proton imbalance to power the synthesis of ATP, which stores the energy until it is needed.

In Boyer's model, the key to this process is a tiny shaft running through the middle of a barrel-like portion of the enzyme. A flow of protons through the membrane makes the shaft spin, which sucks in raw materials and blows out the fresh ATP. The model has been instrumental in overturning simplistic "lock-and-key" explanations of how enzymes work, in which chemicals simply drop into inflexible enzyme grooves, react and then depart.

The other half of the Prize goes to Dr Skou discovered an enzyme which maintains the balance of sodium and potassium ions in the cell. Forty years ago, while experimenting with finely ground crab nerve endings, he discovered the single biggest consumer of ATP in living cells--an enzyme that pumps sodium ions out of cells and potassium ions in. It was the first time anyone had identified an enzyme that moves substances through cell membranes, a key function of all cells.

Both discoveries have shed light on the chemistry of ATP, the molecule that serves as the "energy currency" of living cells.

The energy released when cells break down molecules of fat and carbohydrates is used to create an excess of protons on one side of a membrane. Using ATP synthase, cells harness this proton imbalance to power the synthesis of ATP, which stores the energy until it is needed.

In Boyer's model, the key to this process is a tiny shaft running through the middle of a barrel-like portion of the enzyme. A flow of protons through the membrane makes the shaft spin, which sucks in raw materials and blows out the fresh ATP. The model has been instrumental in overturning simplistic "lock-and-key" explanations of how enzymes work, in which chemicals simply drop into inflexible enzyme grooves, react and then depart.

The structure contains 22722 atoms and 23211 bonds connected as 2987 amino acid groups. These build a 3D protein macro-structure which contains 7 protein chains : A , B , C , D , E , G (this last one is the barrel link shaft which spins, shown better with this view ). The protein structure contains 120 helix units and 94 sheet units and the x-ray structure was found to contain 5 ligated ADP molecules .

Formal Chemical Name (IUPAC)

Picture of ATP synthase

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Picture of ATP synthase



Update by Karl Harrison
(Molecule of the Month for November 1997 )