Tissue distribution of Rab27a and Rab27b. Tissues from perfused mice were lysed, the postnuclear supernatant was ultracentrifuged, and identical amounts of protein (35 μg) from the pellet fractions were subjected to SDS-PAGE and immunoblot analysis as described in Methods. Monoclonal anti-Rab27a Ab 4B12 was used to probe Rab27a (a) and affinity-purified polyclonal anti-Rab27b Ab S086 to probe Rab27b (b). Anti-calnexin Ab recognizing a ubiquitous endoplasmic reticulum-membrane protein (ER-membrane protein) was used as a loading control. Recombinant his₆Rab27a and his₆Rab27b (25 ng) were used as controls for Ab specificity.