Figure 3.

Kinetic analysis of the dephosphorylation of [³²P]DARPP-32 by PP-1. Dephosphorylation of [³²P]DARPP-32 was measured at various concentrations of substrate. The data obtained were plotted using the Lineweaver–Burk method. ▪, Wild-type recombinant PP-1 (K_m, 5.0 μM; V_max, 12.8 μmol·min⁻¹·mg⁻¹); and ○, the values for K_m and V_max for the E275R mutant were determined by extrapolation (dashed line) of the data obtained at 0.5 and 1.0 μM substrate (K_m, 2.9 μM; V_max, 11.1 μmol·min⁻¹·mg⁻¹). The C127S mutant also efficiently dephosphorylated [³²P]DARPP-32 (K_m, 4.2 μM; V_max, 30.8 μmol·min⁻¹·mg⁻¹), exhibiting linear kinetics (data not shown).