Tyrosine is not common at this position in either eukaryotic CuZnSODs (0.5%) or the 34 bacterial enzymes presented in supplementary tables S1–S4, Supplementary Material online (9%) but occupation of this cavity with small molecules has been explored as a route to homodimer stabilization for SOD1-related ALS therapy (Ray et al. 2005; Wright et al. 2013). Here, SOD1 is linked to amyotrophic lateral sclerosis.