You Treat Some Cells with a Proteolytic Enzyme That Is

You treat some cells with a proteolytic enzyme that is too large to penetrate the cell membrane (Set 1) . Another group of cells is made permeable to the enzyme before treatment with the enzyme (Set 2) . A third set of cells was not treated with the enzyme at all (controls) . Proteins are then extracted from the three different sets of cells and applied to an SDS-PAGE gel. Protein W migrates to the same distance on a gel of proteins from Set 1 and Set 2; Protein W migrates a shorter distance on gels of proteins extracted from the control group than on gels of proteins extracted from Set 1 and Set 2 treated cells. Protein X migrates to the same distance on a gel of proteins from control cells and the gels of the proteins from Set 1 and Set 2. Protein Y migrates a longer distance when extracted from Set 1 cells than does protein Y in the controls; Protein Y moves an even larger distance in the gel of the extracts from Set 2. Protein Z migrates the same distance on gels of proteins from the controls and the proteins extracted from Set 1, but it migrates a longer distance in extracts from Set 2 cells. Which protein is exposed only on the exterior of the cell?

A) Protein W
B) Protein X
C) Protein Y
D) Protein Z