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Báo cáo sinh học: "What is cooperativity"

Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học Journal of Biology đề tài: What is cooperativity? | Journal of Biology BloMed Central Question Answer Q A Cooperativity James E Ferrell Jr What is cooperativity Cooperativity is a type of behavior where a number of seemingly independent components of a system act collectively in unison or near-unison. Think of a school of fish a flock of birds or a pack of lemmings. Cooperativity implies some sort of communication among the system s seemingly independent components. In biochemistry the term cooperativity is almost always used in one particular context binding-dissociation reactions at equilibrium. The classic example is the binding of oxygen to hemoglobin Figure 1 . But cooperativity is also important in cell-cell signaling transcriptional regulation and more complex processes governing the behavior of cells. Figure I The oxygen-transporting protein hemoglobin a tetrameric protein consisting of four globin subunits with four oxygen-binding hemes. Reproduced with permission from Michael W King. What is the importance of cooperativity That depends on the system but let s take hemoglobin. Hemoglobin s mission is to pick up a large amount of oxygen in the lungs where the oxygen concentration or partial pressure is about 100 torr and then drop off a good Address Department of Chemical and Systems Biology Stanford University School of Medicine Stanford CA 94305-5174 USA. Email james.ferrell@stanford.edu fraction of it in the peripheral tissues where the oxygen concentration is about 20 torr. Cooperativity helps make this transport efficient. To see why first suppose that hemoglobin were a monomeric oxygen binding protein Figure 2 . Figure 2 Monomeric oxygen-transporting protein. If the binding and dissociation reactions are described by simple mass action kinetics then hemoglobin s oxygen saturation at equilibrium would be given by the Langmuir equation x y - K x where y is the oxygen saturation x is the partial pressure of oxygen and K is the dissociation constant. Because this equation is identical in form to the .