The two vesicle fractions are either untreated (-) or are incubated with the protease trypsin (+). The membrane vesicles are then washed, the membranes solubilized and the proteins denatured and analyzed by SDS gel electrophoresis and Western blotting using polyclonal antibodies against glycophorin A, an erythrocyte plasma membrane protein. The following data are obtained:
What can be deduced from these data about the structure of glycophorin A