Review Question - QID 214636

A scientist is studying the process by which a certain substance is transported through the body. She recreates the process by creating an artificial membrane bilayer separating 2 test chambers and introducing all the normal protein constituents of the membrane. In order to verify that she has reproduced the system, she creates physiologic resting gradients of all ions across the membrane and adds ATP. She finds that the substance she is studying is successfully transported across the membrane. She next removes ATP from the system and finds that the transport continues to occur. She then equalizes all other ion concentrations except for the substance being studied and finds that transport continues to occur in the same direction as before. Finally, she strips the membrane of proteins and finds that the transport ceases. Which of the following proteins and substances is most likely being studied in this case?