Figure 5. ¹H-¹⁵N HSQC spectra of ¹⁵N Myc upon addition of ¹⁴N CaM (1:1).

A. Overlay of HSQC spectra recorded with ¹⁵N Myc free in solution (red) and with equal amounts of Myc and CaM (blue). The zoomed inlet shows a section of the spectrum where peak overlap was relatively low. All measurements were carried out with an excess of Ca²⁺ over calmodulin. B. The intensity ratio between the free and CaM-bound form of ¹⁵N Myc peaks is plotted according to the residue position (I: peak intensity of ¹⁵N Myc with ¹⁴N calmodulin present, I₀: peak intensity of ¹⁵N Myc free in solution). C. The change in the observed peak position upon addition of ¹⁴N CaM to ¹⁵N Myc is plotted according to the residue position. Given values correspond to a pseudo ¹H shift (measured ¹H shift + (1/5)*¹⁵N shift) in order not to bias towards mainly ¹⁵N shifting residues. Negative values in either plot indicate that the intensity of an assigned peak position went below noise level upon addition of CaM; positions not assigned or overlapping in the free form were not used and have 0-values. All measurements were carried out with excess Ca²⁺.