Specificity of anti-ArfI antiserum. (A) MU-AF zymogram of native PAGE gel. (B) Native PAGE (silver-stained) gel. (C) Western blot with anti-ArfI antiserum. Lane 1, purified ArfI; lane 2, soluble cell extract (obtained by sonication and centrifugation); lane 3, Triton extract of particulate cell material (obtained by sonication and centrifugation); lane 4, Triton extract of untreated whole cells; lane 5, concentrated cell-free growth medium. Lanes 1 through 5 contained 0.6, 75.0, 72.5, 60.0, and 72.0 μg of protein, respectively.