Solvent isotope effects on NMR spectral parameters in high-spin ferric hemoproteins: an indirect probe for distal hydrogen bonding.
The influence of solvent isotope composition on 1H-NMR resonance position and linewidth of heme methyls has been investigated for a variety of high-spin ferric hemoproteins for the purpose of detecting hydrogen-bonding interactions in the heme cavity. Consistently larger hyperfine shifts and paramagnetic linewidths in 2H2O than 1H2O are observed for metmyoglobins and methemoglobin possessing a coordinated water molecule. The analysis of the dynamics of labile proton exchange in sperm whale metmyoglobin, and the absence of any isotope effects in the five-coordinate Aplysia metmyoglobin, indicate that the significant axial modulation of heme electronic structure by solvent isotope is consistent with arising from distal hydrogen-bonding interactions. The presence or absence of similarly large isotope effects on shifts and linewidths in other hemoproteins, depending on the presence of a bound water in the distal heme pocket, suggests that this isotope effect can serve as a probe for the presence of such bound water. The absence of any detectable isotope effect on either shifts or linewidths in resting-state horseradish peroxidase supports a five-coordinate structure with bound water absent from the vicinity of the iron.
La Mar
G N
GN
Department of Chemistry, University of California, Davis 95616.
Chatfield
M J
MJ
Peyton
D H
DH
de Ropp
J S
JS
Smith
W S
WS
Krishnamoorthi
R
R
Satterlee
J D
JD
Erman
J E
JE
D000818:Animals; D003574:Cytochrome c Group / Q000378:metabolism; D003578:Cytochrome-c Peroxidase / Q000378:metabolism; D006420:Hemeproteins / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D006735:Horseradish Peroxidase / Q000378:metabolism; D006801:Humans; D006859:Hydrogen; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008786:Metmyoglobin / Q000378:metabolism; D009211:Myoglobin / Q000031:analogs & derivatives / Q000378:metabolism; D011487:Protein Conformation
D003574:Cytochrome c Group; D006420:Hemeproteins; D006454:Hemoglobins; D009211:Myoglobin; C043848:sulfmyoglobin; D008786:Metmyoglobin; D006859:Hydrogen; D006735:Horseradish Peroxidase; D003578:Cytochrome-c Peroxidase