Purification and subunit composition of a GTP-binding protein from maize root plasma membranes

When frozen plasma membranes isolated from maize seedling roots are thawed, a significant portion of GTP-binding activity goes into solution. The GTP-binding protein was purified by ion exchange chromatography on Mono-Q and gel filtration on Superose 6. Its molecular weight was estimated at 61 kDa by gel filtration. The same molecular weight was obtained upon solubilization of the GTP-binding protein with cholic acid followed by gel filtration in the presence of this detergent. SDS-PAGE demonstrated that the isolated GTP-binding protein consists of two types of subunit of molecular weights 27 kDa and 34 kDa.