Fig. 2. Time course of [³H]GDP and [³⁵S]GTPS binding to myr-Arf1p and myr-arf1-17p. Purified Arf1p or arf1-17p (1.25 µM each) was mixed with 10 µM [³H]GDP (circle) or [³⁵S]GTPS (triangle) at 23°C (closed circles and triangles) and 30°C (open circles and triangles). At appropriate time intervals, aliquots of the reaction mixture were filtrated through a nitrocellulose membrane filter and then the radioactivity of the bound nucleotide was measured by scintillation counting.