1. Place ARNO vial on ice and dilute to 0.30 ug/ul (8 uM) with ice cold Exchange Buffer.
2. Dilute Arf protein to 1.25 ug/ul (50 uM) with ice cold Exchange Buffer.
3. Add the following components together in a fresh 15 ml Falcon tube and mix well by pipetting or gentle vortex:
Component ul per well
Exchange Buffer 75
50 uM?Arf 5
8 uM ARNO 10
Note: For a total mixture volume, multiply the volume of reagents per well by the number of wells in the experiment, plus add 20% volume for pipetting losses.
4. Incubate for 20 min at room temperature (RT).
5. Lock in the nucleotide by adding 10 ul (per well) of 50 mM MgCl2.
6. Set up the fluorimeter with Excitation wavelength at 485 nm +/-15 nm and emission wavelength at 525 nm +/- 15 nm at RT.
7. Aliquot the pre-loaded mixture to the assigned wells and place the plate in the fluorimeter.
8. After 5 cycles (150 seconds), place the program on Hold or Pause, and remove the plate.
9. Pipette 10 ul of a) 5 mM GTP solution, b) a small compound, c) a test protein, d) 4 mM EDTA (+ve exchange control) or e) Dilution Buffer (negative control) in respective wells and immediately pipette up and down twice and resume reading for 20 minutes.
10. Save the readings after the kinetic protocols are finished. The exchange rate can be calculated by reducing the data to max slope (using 12 pts) or Vmax with the software that accompanies the plate reader. The exchange curve can be achieved by export to Microsoft Excel.