GTP-BINDING PROTEINS IN PLASMA-MEMBRANES OF LOACH EMBRYONIC-CELLS

The activity of high affinity GTPase in purified plasma membranes of l each embryonic cells (11-12 h of development at 21 degrees C) has been found. The Kit of this GTPase amounts to 6.7 . 10(-7) M which corresp onds to the K-m of other known GTP-binding proteins (G-proteins). Bact erial ADP-ribosyltransferases has been used for identification of G-pr oteins. It was shown that pertussis toxin catalyzes the incorporation of P-32-labeled ADP-ribose into 39 kD protein. Exoenzyme C3 of Botulin icum clostridium modifies two proteins of 27 and 29 kD. Substrates for cholera toxin have not been detected under our experimental condition s. Using GTP-blotting technique, we identified several small molecular weight G-proteins (SMG-proteins), two of them, p24 and p26, were domi nant. Binding of [alpha-P-32]GTP to these proteins depends on the Mg2 and is completely inhibited in the presence of non-labeled GTP. Using polyclonal antibody against p21(ras) ras-related protein p23 was iden tified. The possible role of the revealed G-proteins in regulation of cell proliferation and differentiation during early embryogenesis is d iscussed.