Subcellular localization of reticulocyte AQP-1. Constituents of mouse reticulocytes were fractionated after lysis as described in “Methods.” The various fractions (50 μg protein), plasma membrane, endosomes, cytosol, and exosomes were separated by SDS-PAGE and (A) stained with Coomassie Blue or (B) immunoblotted for the proteins indicated. Arrows indicate cytoskeleton proteins present in the mature red cell plasma membrane. Blots of plasma membrane fraction were exposed for a shorter period of time than those of the other 3 samples as indicated by the solid lines.