Detection of small GTP-binding proteins in the outer envelope membrane of pea chloroplasts

Abstract

We found small GTP-binding proteins in the outer envelope membrane of pea chloroplasts. The proteins in this membrane were separated by SDS-PAGE, transferred to a nitrocellulose filter, and incubated with [α- 23P]GTP. Three GTP-binding proteins with the molecular weight of 24 000 were found. Binding was prevented by 10 −8—10 −7 M GTP or by 10 −7 M guanosine 5′-[γ-thio]triphosphate or GDP; binding was unaffected by 10 −8—10 −6 M ATP. Thermolysin treatment of intact chloroplasts resulted in the loss of GTP-binding activity, suggesting that these proteins were in the cytosolic side of the outer envelope membrane.