Fig. 2. Localization of Gβ in dark-adapted and illuminated Blepharisma by cell fractionation and immunoblotting. Lysates from dark-adapted (lanes 1, 3 and 5) and illuminated (lanes 2, 4 and 6) cells were fractionated by centrifugation and Gβ was detected in the separate fractions by immunoblotting with specific antibody against Gβ. Results indicate interaction of the antibody with protein bands of 32 kDa in the membranous fractions (lanes 3 and 4) and 36 kDa in the cytoplasmic fractions (lanes 5 and 6). Lane 7 shows immunoblots identifying Gβ in whole cell lysate from the rod outer segment (ROS) of bovine photoreceptor cells. Blotting with β-tubulin antibody was used as a test of equal protein loading. Lower panel shows a densitometric quantification diagram of Gβ levels in lysate and cell fractions under different light conditions (filled and open bars correspond to 32 kDa and 36 kDa, respectively). The level of Gβ in lysate from the control dark-adapted cells was taken as 100%. Bars represent mean values ± s.e.m. of four experiments.