title: Calmodulin: calcium, potassium, and magnesium ion multiple equilibria and kinetics for interconversion, including the effect of repeated stimulation.
abstract: Using computer simulations, with realistic values for the intrinsic thermodynamic binding constants and kinetic on and off rate constants at the four metal-binding sites, the calmodulin molecule is shown to have been optimally adjusted by evolution for biological function. Despite a very large number of potential molecular states, depending upon occupation by potassium, calcium, or magnesium ions, the system restricts itself to a small number of physiologically-significant equilibrium species. It appears to possess built-in triggers for biological processes, with rapid (approximately 20 ms time-scale), step-function shaped, changes of the populations of the CMKK, CMMK, CKKK, CMMM (and CCKK) states. The time-response of calmodulin to periodic changes in ionic levels (2 and 5 s-1) makes it quite adequate for repeated stimulations. In short, calmodulin appears as a very selective information transmitter at the molecular level.
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D003201:Computers; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism*; D013268:Stimulation, Chemical
chemical_list: D002147:Calmodulin; D008274:Magnesium; D011188:Potassium; D002118:Calcium