Open AccessDynamics of heme iron in crystals of metmyoglobin and deoxymyoglobin.
Author(s) -
E. R. Bauminger,
S. Cohen,
I. Nowik,
S. Ofer,
J. Yariv
Publication year - 1983
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.80.3.736
Subject(s) - metmyoglobin , brownian motion , chemistry , mean squared displacement , myoglobin , diffusion , relaxation (psychology) , nuclear magnetic resonance , harmonic oscillator , displacement (psychology) , fick's laws of diffusion , protein dynamics , crystallography , molecular physics , thermodynamics , physics , molecular dynamics , computational chemistry , quantum mechanics , psychology , social psychology , organic chemistry , psychotherapist
The 57Fe gamma-ray resonance absorption spectra have been measured in crystals of metmyoglobin and deoxymyoglobin over a wide range of temperatures. Above a critical temperature common to both proteins (220 K), the dynamics of heme iron display a dramatic change, in that two kinds of thermal fluctuations come into play--a fast fluctuation associated with a steep decrease of the total fluctuation of characteristic time 10(-8) sec, associated with bounded diffusive motion. By using both discrete jump and continuous diffusion models, the latter based on the Brownian motion of an overdamped harmonic oscillator, the essential parameters of the iron motion (mean square displacement and jump frequency or diffusion constant) can be derived as a function of temperature. Thus, for deoxy Mb at 288 K, the mean square displacement for the fast fluctuation is about 6 X 10(-2) A2 and for the diffusive motion is 1.6 X 10(-2) A2; the diffusion constant is 4 X 10(-10) cm2/sec. The diffusive process is associated with an activation energy of about 0.75 kcal/mol. Although the same general kinds of phenomena are observed in crystals of MetMb and deoxy Mb, significant differences in behavior are found, which suggest that the main dynamical phenomenon observed reflects internal large-scale motions of the protein.