Expression of Rab27a and Rab27b in melanocytes and platelets. Platelets from wild-type (C3H/He^+/+), homozygous (ash/ash), and heterozygous (+/ash) ashen mice and a melanocytic cell line (melan-a) were lysed, and identical amounts of protein (13 μg) from total lysates (for platelets) or postnuclear supernatants (for melan-a cells) were subjected to SDS-PAGE and immunoblotting 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 ER-membrane protein was used as a loading control.