Related structure solved of the only membrane-embedded enzyme of the citric acid cycle / Key function in metabolism New insights into the mechanism of the hub of metabolism, the citric acid cycle, have been obtained by scientists at the Max Planck Institute of Biophysics and the Institute of Microbiology of the J. W. Goethe University, both located in Frankfurt am Main, Germany. Using X-ray crystallography, they have determined the three-dimensional structure of an enzyme related to succinate dehydrogenase, a key enzyme in the citric acid cycle (nature, 25 November, 1999).
Life is work and requires energy, that is also true at a cellular level. In order to fulfill their various tasks, cells make use of the energy stored in organic molecules. With the help of their enzymes, they systematically break down complex organic molecules and form more simple, less energy-rich, products.
The most efficient and most frequently used way involves cellular respiration. This commences with glucose or other organic compounds. Consuming oxygen, it eventually generates water, carbon dioxide, and in particular also energy-rich ATP and heat. The cellular generation of energy encompasses three metabolic pathways: glycolysis, the citric acid cycle, and the respiratory chain. The first two pathways, glycolysis and the citric acid cycle, break down glucose and other organic compounds in a step-wise manner. In the respiratory chain, the energy is released and can be used by the mitochondria for the generation of the energy "currency" ATP.
The citric acid cycle or Krebs' cycle is the hub of metabolism. It is responsible for the catabolism of carbohydrates, fatty acids and amino acids, and it is also an important source of intermediates for the production of other biochemical compounds. One of the key enzymes in this process is succinate dehydrogenase. It is embedded in the mitochondrial membrane and couples the citric acid cycle to the respiratory chain. The coupled action
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