Dynamics in globular proteins: vibrational echo experiments

The temperature-dependent vibrational pure dephasing of the CO stretching m ode of carbonmonoxyhemoglobin (HbCO) in an ethylene glycol:water mixture is reported and compared to previously measured dephasing of carbonmonoxymyog lobin (MbCO). HbCO displays a T-1.3-dependent pure dephasing rate between 1 5 and similar to 150 K, suggesting glass-like behavior. Above 150 K, the te mperature dependence becomes steeper. The functional form of the HbCO and M bCO pure dephasing temperature dependences are identical within error. Howe ver, the hemoglobin pure dephasing is 27% smaller at all temperatures studi ed, suggesting that the fast dynamics or the protein electric field-CO coup ling is smaller in hemoglobin than in myoglobin. (C) 2000 Elsevier Science B.V. All rights reserved.