Differential stimulation of the GTPase activity of G-proteins by polylysine

Abstract

Polylysine, polyornithine and, to a lesser extent, polyarginine were found to stimulate the GTPase activity of the purified recombinant α subunit of the human Gi-3 transducing protein αi-3. Optimal stimulation of 4- to 5-fold was obtained with polysine concentrations between 1 and 20 μM, higher concentrations being inhibitory. Polylysine at similar concentrations stimulated by 50% the GTPase of transducin (gt), the vision transducing protein, but had only a very slight effect on the GTPase of the p21 product of the H-ras protooncogene. The stimulation of the αi-3 GTPase caused by polylysine was due to a reduction of the apparent Km for GTP from 3.8 to 1.3 μM. The stimulation by polylysine was observed at free Mg2+ concentrations below 1 μM. These results indicate that polylysine acts in a fashion similar to mastoparan and substance P in mimicking the action of an agonist-bound receptor on G-proteins. © 1992.