)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 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?