Nelfinavir Mesylate (Viracept) is an effective HIV protease inhibitor (Ki: 2 nM).

HIV protease:2 nM(Ki)

GTPγ[35S] binding assay: The cells are homogenized and centrifuged at 26900 × g for 30 min at 4°C. Membranes are re-suspended in 20 mM HEPES (pH 7.4), 100 mM NaCl, 10 mM MgCl2, 1 mM EDTA and 0.1% fat-free BSA at 2–3 mg protein/mL. GTPγ[35S] binding assay is performed with the membranes (75 mg protein /mL in 50 mM HEPES, 100 mM NaCl, 10 mM MgCl2, 20 μg/mL saponin and 0.1% fat-free BSA (pH 7.4), 5 mg/mL with wheat-germ agglutinin-coated scintillation proximity assay-bead, and 10 μM GDP for 10–15 min. The GTPγ[35S]-binding reaction is started by the addition of 200 pM GTPγ[35S]. After 120 min at room temperature, the plates are centrifuged for 10 min at 300 × g and counted.