Figure 1.

(a) Normalized vT-ESI mass spectra of hMb (in 10 mM NH₄OAc, pH = 4.5) at solution temperatures of 28, 63, and 93 °C. Heme-bound hMb states are indicated by filled black circles and heme-free aMb species with open circles. (b) Temperature-dependent stability curves derived from the formation of aMb (blue diamonds) on the left axis and the average charge state plots of ${\overline{z}}_{\text{all}}$ (open black squares), ${\overline{z}}_{\text{apo}}$ (open black circles), and ${\overline{z}}_{\text{holo}}$ (filled black circles). Data points from T = 28 to 42 °C are excluded in the model of ${\overline{z}}_{\text{apo}}$ due to low signal/noise. (c.) Temperature-dependent CD spectra of hMb (in 10 mM NH₄OAc, pH = 4.5) with the characteristic negative α-helix peak at 222 nm indicated with a dotted line. (d) Comparison of loss of α-helical structure measured by CD (red triangles) with formation of aMb from MS measurements (blue diamonds).