Fig. 1.

a Isotope Labelling panel showing the way in which a protein sample (in this case an SH3 domain) can be designated as being uniformly [¹³C,¹⁵N] labelled (upper panel, Sample 1) or composed of 50% [U-¹³C] and 50% [U-¹⁵N] labelled protein (upper panel, Sample 2 and lower panel). The ‘Experiments’ column in the upper panel shows which experiments are associated with each sample. b Diagram illustrating the composition of Sample 1. c Diagram illustrating the composition of Sample 2