Motional freedom of the central metal atom in apohemoglobin reconstituted with 111In: protoporphyrin IX. Time-differential perturbed gamma-ray angular correlations

Abstract

Based on time-differential perturbed gamma–gamma angular correlations (PAC), the rotational correlation time for indium-111 in apohemoglobin reconstituted with 111In:protoporphyrin IX is τrot(Hb)=23 ns. For 111In:mesoprotoporphyrin IX reconstituted similarly into apomyoglobin, PAC measurements yield τrot(Mb)=16 ns. The PAC ratio τrot(Hb)/τrot(Mb)=1.4 is the same (within experimental error) as that from fluorescence polarization (FP) measurements for apo-Hb and apo-Mb reconstituted with an aminonaphthalene sulfonate in place of the natural heme. Since the rigid-sphere ratio τrot(Hb)/τrot (Mb)=4.0 is larger than the experimental PAC and FP ratios, the metalloporphyrin exhibits significantly more internal motional freedom in hemoglobin than in myoglobin. Finally, PAC quadrupolar asymmetry parameter values show that the electron distribution about the central metal atom is axially symmetric in reconstituted In–Mb, but not in reconstituted In–Hb.

Selective binding of antimicrobial porphyrins to the heme‐receptor IsdH‐NEAT3 of Staphylococcus aureus

“…We distinguished between these two alternatives by using indium(III), which is an ion ∼25% larger than iron(III) and gallium(III) . Indium displays a stable oxidation state (III) when incorporated in the porphyrinate molecule . Binding assays (UV–visible and ITC), X‐ray crystallography, and functional assays indicates that In(III)‐PPIX closely mimic the properties of heme.…”

Myoglobin and hemoglobin rotational diffusion in the cell

“…Moreover, the Hb/Mb Tr ratio of 3.9 is in excellent agreement with the value predicted from the Stokes-Einstein equation as the molecular volume of globular proteins scales up from a monomeric to a tetrameric form. No Hb fluctuation in the heme pocket is apparent, which would give rise to a Hb/Mb Tr ratio of 1.4, as detected in perturbed angular correlation studies (Marshall et al, 1980(Marshall et al, , 1983…”

“…The Stokes-Einstein equation for rotational diffusion wTr= -kT 2where r is the molecular radius, q is the solvent viscosity, k is Boltzmann's constant, and T is the temperature in Kelvins, provides then a theoretical basis to compare the NMR determined Tr against values obtained from other physical methods Marshall et al, 1983).…”

Perturbed angular correlation spectroscopy and its application to metal sites in proteins: possibilities and limitations

“…Since then a large number of such investigations have been performed. Some of the more recent ones are listed here (Demille et al 1979;Kalfas et al 1980;Marshall, Lee & Martin, 1980;Martin, Kalfas & Skov, 1978;Martin, El-Kateb & Kuhnlein, 1982;Marshall, Lee & Martin, 1983).…”