Figure 2.

(A) Cyclization of 3 and deuterated probes 3^3d, 3^5d, and 3^3/5d by P450_Blt and Blt mutants to form 6. (B) MS¹ isotope cluster for 6B^3d, 6B^5d, and 6B^3/5d that agrees with the formation of a YXY cross-link via the Y-5 phenol moiety in 6B by the Blt-M3 mutant, as is revealed by the loss of 1 deuterium atom from 6B^3d and 6B^3/5d but not from 6B^5d. (C) Upfield region (extract) of the ¹H NMR spectrum of 6B, with peaks assigned (700 MHz, DMSO-d₆). (D) Key HMBC correlations used to establish the cross-link as Tyr₃C-Tyr₅O in 6B overlaid with an HMBC spectrum extract illustrating key correlations to Tyr₃ C1″. For full correlations and spectra, see the SI.