Figure 1

G proteins on endosomes and membranes. A) Quantitative distribution of G_sα, G_iα1,2, G_iα3 and G_β in different cell fractions: CM (white bars), BLM (gray bars), liver homogenate (dotted bars), RRC (black bars), CURL (down slashed bars), MVB (up slashed bars) and lysosomes (stripped bars). Optical density of bands for each cell fraction on a single blot were expressed as a fraction of the optical density of the band for CM on the same blot and bars represent the mean ± SEM of results from "n" different preparations of each cell fraction, as indicated on the figure. Except for G_ia1,2 in BLM, G protein subunits were enriched significantly in CM and BLM compared to homogenate (p < 0.0006). G protein subunits in endosomes and lysosomes were significantly less than in CM or BLM (p < 0.0001 to p = 0.027). In vesicles G_sα, G_iα1,2, and G_β were found in the order RRC > CURL > MVB > lysosomes and G_iα3 in the order RRC > CURL, MVB > lysosomes. Many of these differences achieved statistical significance: G_sα : RRC vs MVB, p = 0.027; RRC vs lysosomes, p = 0.007; CURL vs lysosomes, p = 0.049. G_iα1,2: RRC vs CURL, p = 0.05; RRC vs lysosomes, p = 0.022. G_iα3: RRC vs lysosomes, p = 0.01. G_β : RRC vs CURL, p = 0.032; RRC vs MVB, p = 0.002; RRC vs lysosomes, p = 0.0006; CURL vs lysosomes, p = 0.008. B) Representative Western blots illustrating data summarized in (A). G_sα : 15 μg protein/lane; others: 30 μg protein/lane; Hom: homogenate.