Fig. 4

The competition hypothesis used for explaining the Parabola Principle. a-c The situations of low, optimum, and high ratios of SPs to SPBPs. d The situation involving the decreasing ratio of SPs to SPBPs by the introduction of additional copy numbers of SPBP-eGFP units. e-f The eGFP RFI per OD of a series of pMetalMultiGFP biosensors when incubated with 20, and 40 μmol/L of Cd (II), respectively