A transmembrane protein has the following properties: it has two binding sites, one for solute A and one for solute B. the protein can undergo a conformational change to switch between two states: either both binding sites are exposed exclusively on one side of the membrane, or both are exposed exclusively on the other side of the membrane. The protein can switch between the two conformational states only if both binding sites are occupied or if both binding sites are empty, but cannot switch if only one binding site is occupied.

A. What kind of a transporter do these properties define?

B. Do you need to specify any additional properties to turn this protein into a transporter that couples the movement of solute A up its concentration gradient to the movement of solute B down its electrochemical gradient?