Recombinant full-length human MEKK3 was expressed by baculovirus in Sf9 insect cells using an N-terminal GST tag. MEKK3 is a member of the MEKK family of protein kinases that directly regulate SAPK and ERK pathway but not the p38 pathway. MEKK3 modulates SAPK and ERK activity by activating the upstream targets SEK and MEK1/2, respectively. KSR2 can regulate the activity of MEKK3 and can reduce MEKK3-mediated ERK activation. ADP-Glo Kinase Assay is a luminescent kinase assay that measures ADP formed from a kinase reaction; ADP is converted into ATP, which is a substrate in a reaction catalyzed by Ultra-Glo Luciferase that produces light. The luminescent signal positively correlates with ADP amount and kinase activity. The assay is well suited for measuring the effects chemical compounds have on the activity of a broad range of purified kinases, making it ideal for both primary screening as well as kinase selectivity profiling. The ADP-Glo Kinase Assay can be used to monitor the activity of virtually any ADP-generating enzyme (e.g., kinase or ATPase) using up to 1mM ATP.