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. 2012 Dec;140(6):595–597. doi: 10.1085/jgp.201210926

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© 2012 Andersen

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Figure 1. — A general scheme for allosteric binding of a ligand (A) to a tetrameric protein, where each subunit can exist in two states: T, represented by squares, and R, represented by circles. This general model encompasses both the MWC model, which is represented by quaternary conformational transitions between the red columns at the extreme left and right in the scheme, and the KNF model, which is represented by the top/left and the bottom/right red states plus the blue oligomers on the top/left to bottom/right diagonal. (The scheme does not include states that differ only in placement of A in the T or R subunits of a state with n T and [4 – n] R subunits [0 ≤ n ≤ 4], meaning that the complete scheme includes 44 states, rather than the 36 depicted here.) Modified after Eigen (1968).