A NONIONIC VESICLE LIPID ENHANCES MASTOPARAN-STIMULATED GTPASE ACTIVITY OF HETEROTRIMERIC G-PROTEINS

Isolated heterotrimeric G-proteins exhibit full biological activity wh en reconstituted into liposomes. Here, we investigated the nonionic su rfactant macrogol-260-cetylstearylether (TA 6) as an efficient vehicle for the reconstitution of G-proteins. Reconstitution efficiency of G- proteins was recorded by GTP gamma S-binding. Their biolog potency was measured as basal and mastoparan-stimulated GTPase-activity. G-protei ns were fully active when associated with liposomes. On the other hand , G-proteins solubilized by TA 6 micelles or reconstituted into pure T A 6 vesicles exhibited impaired biological activity. However, vesicles containing different ratios of azolectin and non-ionic TA 6 showed ab out 50% higher reconstitution efficiency as compared to pure liposomes . In addition, basal and mastoparan-stimulated GTPase-activity in vesi cles containing an axolectin / TA 6 ratio of 3:1 were 2.7 and 9.1 fold higher than in pure liposomes, respectively. These data emphasize tha t the composition of the lipid membranous environment significantly in fluences G-protein activity.