GTP-binding protein(s) in green plant, Lemna paucicostata

GTP-binding protein(s) assayed by [35S]GTP gamma S was detected in the extract of Lemna paucicostata containing membrane components. About 15% of [35S]GTP gamma S activated GTP-binding protein, separated from unbound [35S]GTP gamma S by gel filtration, was retained on Millipore HAWP membrane filter. 80% of [35S]GTP gamma S activated protein, mixed with charcoal solution, remained in the supernatant after centrifugation of the mixture. Successive treatments of the assay mixture by charcoal solution established the assay system for the activation of GTP-binding protein. The Km value for the activation of GTP-binding protein was 8 nM.