FIGURE 3.

The normalized ratio, () plotted versus the ¹⁵N-{¹H} NOE for the experimental CaM relaxation data. The normalization constant is RT₁ in the absence of any internal motion. was calculated with a ¹⁵N CSA of −170 ppm and a of 10 ns, the average overall tumbling time for the CaM dimer (vide infra). RT₁ was also corrected for the linear NOE dependence for fast (<200 ps) internal motion. The contours of the theoretical are shown for a one-contribution model (solid black contours), and a two-contribution model (dotted red contours). In both theoretical models, τ_if is running from 20 ps to 6 ns. In the two-contribution model, an additional 2.5 ns internal motion is present with = 0.8. Guidelines for internal motions of 1.0 and 2.5 ns for the one-contribution model is outlined with dashed black lines. The experimental CaM data are overlaid on top of theoretical curves, and are normalized with the same as the theoretical curves. The average error in the and is 1.0 and 2.5%, respectively. Hence, the error in the experimental equals 3.5%. The shaded area represents the area where residues are only affected by picosecond-timescale internal motion, i.e., motions < 200 ps. curves are not affected by exchange contributions, have relatively small error margins, and are only weakly affected by variation in the CSA and overall rotation time. Thus, average approximate values for these parameters can be used without adversely affecting the correctness of the drawn conclusions.