Hydration of apomyoglobin in native, molten globule, and unfolded states by using microwave dielectric spectroscopy.
The high resolution dielectric spectra of semidilute solutions of apomyoglobin in native (N, pH = 5), acid-induced molten globule (A, pH = 4), and unfolded (U(A), pH = 3) states have been measured in the range from 0.2 to 20 GHz. Based on a two-component mixture theory, we obtained the following hydration numbers per protein molecule: 590 +/- 65 for N, 630 +/- 73 for A, and 1110 +/- 67 for U(A). There was no clear difference between N and A states in contrast to the 25% reduction of helix content and the 50% reduction of heat capacity change upon unfolding. This suggests that the association of hydrophobic moieties might follow the disruption of secondary structures from N to A states. The measured hydration number of U(A) was close to that of the accessible water number (1340) of a protein molecule calculated for a fully extended structure, indicating that the structure of U(A) is extended but somewhat more compact than that of a fully extended state.
Kamei
Takashi
T
Department of Metallurgy, Graduate School of Engineering, Tohoku University, Aoba-yama 02, Sendai, 980-8579, Japan.
Oobatake
Motohisa
M
Suzuki
Makoto
M
D000818:Animals; D001059:Apoproteins / Q000737:chemistry*; D004563:Electrochemistry / Q000379:methods; D006736:Horses; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D015203:Reproducibility of Results; D014867:Water
D001059:Apoproteins; D009211:Myoglobin; C010857:apomyoglobin; D014867:Water