Fig. 5.

Determination of turnover number for autophosphorylation of CaMKII in the presence of WT and mutant CaMs. The time course of autophosphorylation of CaMKII was determined in saturating Ca²⁺/CaM. Data were gathered with a Quench Flow apparatus and normalized as described in Methods, then fit with the equation: A(1 − e^{−k_p(t − t₀)}), where k_p is the turnover rate (unknown), t₀ (a negative term) is the time at which the extrapolated autophosphorylation curve crosses the x axis (Supporting Text), and A is a scaling factor. A, k_p, and t₀ were fit simultaneously by nonlinear regression performed with the Levenberg–Marquardt method in Mathematica. The k_p values supported by each form of CaM are summarized in Table 2. Data were obtained from five experiments with WT CaM, five with CaM-C^WT, and three with CaM-N^WT. WT CaM (●), CaM-C^WT (▿), and CaM-N^WT (▴).