FIG. 6.

In vitro kinase activity of Leu115 substitution mutants. Leu115 substitution variants were assayed in vitro with increasing concentrations of PD 184352 as described. Only the alanine substitution was inhibited (IC₅₀ = 0.68 μM) at a 10-fold higher concentration than that required for wild-type MEK (IC₅₀ = 0.067 μM). The constructs assayed included the wild-type (○), Leu115Ala (•), Leu115Glu (□), Leu115Pro (▪), Leu115Arg (▵), and Leu115Trp (▴) constructs. These data represent two independent experiments. The 100% control value reflects the Raf-activated, untreated enzyme activity.