Separation of integral and membrane associated proteins. The total Synechocystis membranes were treated with 8.0 M urea to release the membrane associated proteins. The supernatants containing the released membrane associated proteins were collected as the peripheral fraction after centrifugation, and the insoluble pellet was collected as the integral fraction. The proteins in the peripheral fraction were further precipitated with 10% TCA, washed with ice-cold acetone, and re-solubilized by the multi-surfactant solution. The integral proteins were directly washed with acetone and solubilized with the same volume of multi-surfactant solution. Equal volume of samples from the peripheral fraction (Lane P) and the integral fraction (Lane I) were separated by SDS-PAGE. Total membranes containing 10 μg of chlorophyll were used as the loading control (Lane T). All the samples were incubated with denaturing dye (2% SDS and 0.1 M DTT) at room temperature for 4 h before separated by SDS-PAGE.