For the in vitro experiments, guanosine 5′ diphosphate (GDP), bovine serum albumin (BSA), and adenosine deaminase were purchased from Sigma-Aldrich. GTPγS was purchased from Roche Diagnostics (Branchburg, NJ). [35S]GTPγS (1150–1300 Ci/mmol) was obtained from Perkin Elmer Life Sciences (Boston, MA). Scintillation fluid (ScinitSafe Econo 1) was purchased from Fisher Scientific (Pittsburgh, PA).
