The GTP-binding regulatory proteins of neuroblastoma × glioma, NG108-15, and glioma, C6, cells Immunochemical evidence of a pertussis toxin substrate that is neither Ni nor No

AbstractAmounts of the guanine nucleotide binding regulatory proteins which are also pertussis toxin substrates (such as Ni and No) were measured in rat glioma, C6BU-1, cells and in neuroblastoma × glioma, NG108-15, hybrid cells. Measurements were performed both by quantitating pertussis toxin catalyzed ADP-ribosylation and by quantitative immunoblotting with affinity purified antibodies specific for Ni or No. The amounts of pertussis toxin substrate in C6 and NG108-15 cells are 7.5 and 0.6 pmolmg membrane protein, respectively. These levels are minimum values and higher estimates of the total amounts of N proteins in the two cells are obtained by quantitative immunoblot analysis of the β-subunit common to all N proteins. Immunoblots with specific antibodies show that NG108-15 cells contain 3.8 pmolmg of No and detectable but small ( < 0.1 pmolmg) amounts of Ni. In contrast, C6 cell membranes contain no detectable No and only 0.14 pmolmg Ni. Thus, C6 cells contain large amounts of a pertussis toxin substrate which is neither Ni nor No