Figure 2. Low-frequency region of the resonance Raman spectra of the FeIII–NO complexes of saNOS (left) and bsNOS (right).

The spectra were obtained with the L-arginine-free and pterin-free proteins with ¹⁴N¹⁶O (a and j) and ¹⁵N¹⁶O (b and k). The ¹⁴N¹⁶O minus ¹⁵N¹⁶O difference spectra (a minus b and j minus k) are shown in (g) and (p). The spectra of the L-arginine-bound proteins (1 mM) were obtained with ¹⁴N¹⁶O (c and l) and ¹⁵N¹⁶O (d and m). The ¹⁴N¹⁶O minus ¹⁵N¹⁶O difference spectra (c minus d and l minus m) are shown in (h) and (q). The spectra of the L-arginine- and H₄B-bound proteins were obtained with ¹⁴N¹⁶O (e and n) and ¹⁵N¹⁶O (f and o). The ¹⁴N¹⁶O minus ¹⁵N¹⁶O difference spectra (e minus f and n minus o) are shown in (i) and (r).