Figure 1.

1D ¹H/¹³C HMQC NMR spectra of 2 mM {¹³C, ¹⁵N} His-labeled α-lytic protease in 0.1 M KCl and 90% H₂O/10% D₂O at 30°C. (A) Resting α-lytic protease at pH 4.5 (imidazole protonated). (B) Resting α-lytic protease at pH 9.0 (imidazole unprotonated). (C) α-Lytic protease inhibited with ≈2-fold excess MeOSuc-Ala-Ala-Pro-boroVal (AAPbV) at pH 4.5 [imidazole-protonated and spectrum pH-independent over accessible range (3.5–10.5)].