Cooperativity/cooperative effect negative

Both secondary active transport and positive cooperativity effects enhance carrier-mediated solute flux, in contrast to negative cooperativity and inhibition phenomena, which depress this flux. Most secondary active transport in intestinal epithelia is driven by transmembrane ion gradients in which an inorganic cation is cotransported with the solute (usually a nutrient or inorganic anion). Carriers which translocate more than one solute species in the same direction across the membrane are referred to as cotransporters. Carriers which translocate different solutes in opposite directions across the membrane are called countertransporters or exchangers (Figs. 10 and 11). 

A substrate or effector that binds preferentially to the R state increases the concentration of the R state at equilibrium. This can only happen if, in the absence of substrate or effector, the enzyme is predominantly in the T state. If the enzyme were predominantly in the R state to begin with, it would already have increased affinity for the substrate and there would be no allosteric or cooperative effects. Consequently, the MWC model cannot account for negative cooperativity (but this is rare anyway). 

Frumkin isotherms for a few different values of the interaction parameter g. Positive values of g broaden the isotherm because the adsorbed particles repel each other for negative values of g the isotherms are narrow because adsorption is then a cooperative effect. The case g = 0 corresponds to the Langmuir isotherm. 

Dialkyl-substituted anthracene-bridged bis-crown ethers 92 formed 1 1 and 1 2 (crown to metal) complexes with alkali metal ions <1999J(P2)1193>. The stability constants of the latter were suggestive of a negative cooperation effect between the two crown ether units < 0.25). The derivative with R = Et showed a decrease in... 

Louis, T.E. and Jordan, V.C. (2006) Cooperative effect of gefitinib and fumitremorgin C on cell growth and chemosensitivity in estrogen receptor a negative fulvestrant-resistant MCF-7 cells. International Journal of Oncology, 29, 1237-1246. 

Cooperative effects in the restricted rotation of aryl groups in 2,4,6,8-tetraaryl-3,7-diazabicyclo[3.3.1]nonanes have been described it was concluded on the basis of the large, negative value of AS for rotation of the 2(4)... 

An accurate and consistent evaluation of statistical factors in self-assembly processes is of crucial importance to predict the expected stability constant in the absence of cooperative effects and, therefore, to spodight the emergence of either positive or negative cooperativity as a marked deviation firom statistical behaviour. However, the evaluation of statistical factors can be controversial and doubtful sometimes. A critical re-examination of the methods to assess statistical factors in self-assembly processes has been published in 2007. " Two methods appear the most useful, namely, the symmetry number method and the direct counting method. The two methods if properly appHed give the same results however, the symmetry... 

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