How does the chemical potential of the substrate drive a uniporter?

Uniporters are a large class of transporters mediating facilitated diffusion of substrates along the direction of the substrate concentration gradient. Recently, structures of several important uniporters have been reported; however, the precise mechanisms of uniporter function remain subject of debate. Here, we present a series of general thermodynamic descriptions of uniporters, aimed at understanding the structure-function relationship of uniporters, and in particular to reconcile biochemical phenomena of uniporters with our previously proposed thermodynamic model of general transporters.