Purification and some properties of GTP-binding proteins from pig heart plasma membranes

The major GTP-binding proteins (N-proteins) have been purified from cholate extract of pig heart plasma membranes using chromatography through DEAE-Trisacryl, Sephacryl S-300, Octyl-Sepharose, and DEAE-Sepharose. The hydrophobic chromatography resulted in elution of two GTP-binding activity peaks. The specific GTP gamma S binding of both N-protein preparations was 2.5 nmol/mg of protein with KD value 2.10(-7) M. The first preparation contained three polypeptides with molecular masses 40 kDa, 36 kDa, and 23 kDa. 40 kDa polypeptide was ADP-ribosylated by pertussis toxin. The same protein appeared to be the only substrate of pertussis toxin in crude detergent extract of membranes. The major polypeptides of the second preparation were represented by 37 kDa and 23 kDa polypeptides.