The tyrosine ring rotation angle (θ) for the Tyr residues in the DtpAa triple variant, calculated as explained in ref. 50 form the dihedral angles (ϕ₂ = C_α − C_β − C1 − C2 and ϕ₆ = C_α − C_β − C1 − C6) determined from the X-ray structure. The last two columns report the difference between θ and the two complementary angles^a found when using TRSSA-Y.

Tyr number	ϕ 2 (o)	ϕ 6 (o)	θ (o)	|θ − 56.5°|	|θ − 61.5°|
116	−88.49	90.44	59.025	2.525	2.475
272	−87.82	85.23	61.295	4.795	0.205
347	−96.14	87.37	64.385	7.885	2.885
366	−89.5	88.31	60.595	4.095	0.905

^aThe θ = 61.5° gives an identical simulated spectrum as the θ = 56.6° does, due to the symmetry of the two configurations as 56.5° + 61.5° = 118° – the angle between the two methylene protons as shown by DFT calculations.⁸⁴