Fig. 5. ¹⁴N- and ¹⁵N-labelled oligomeric β₂m subunit exchange experiments illustrating the dimer (D) 7+, trimer (T) 10+ and 11+, and tetramer (Q) 13+ ions. Samples of ¹⁴N-WT β₂m (A, C) or ¹⁴N-H51A (B, D) were mixed with ¹⁵N-WT β₂m or ¹⁵N-H51A monomer samples, respectively in a 1 : 1 (v/v) ratio for 1 min (A, B) or 50 min (C, D) at 50% of the individual lag-phases for the two proteins. Peaks corresponding to all ¹⁴N- and all ¹⁵N-oligomers are shown in red, and peaks corresponding to mixed ¹⁴N/¹⁵N oligomers are shown in blue.