chemia - Studia

ADSORPTION OF HORSE METHEMOGLOBIN ON BIOACTIVE GLASS AT HIGH SALT …
salt concentration of the solution. Because protein dissociation was found to be
less pronounced than in low salt conditions, one can conclude that electrostatic
interactions play an important role in the dissociation of methemoglobin
observed when the protein is adsorbed on the bioactive glass.
On the other hand, the total absence of modulation in the DEER
signal on the BG treated with GA can be attributed also to a homogenous
spatial distribution of the spin labels in the sample, as a consequence of
polymerization induced by GA. We assume that in this case, both effects
(dissociation and polymerization of the protein) are contributing to the
overall DEER signal. Hence, after analysis with Tikhonov regularization a
distance distribution could be obtained only for the protein in buffer solution
and for protein adsorbed on BG without GA (figure 3). The Cβ-Cβ distances
between the β-93 sites derived from the structures of the hemoglobin in
solution and in the adsorbed state revealed a defined distance distribution,
with a major distance at 24.8 Å in solution and 35 Å in adsorbed state. This
increasing of major maximum in distance distribution suggests that the two
β chains are slightly apart for the protein in adsorbed state. Projected on
the protein, this means that in adsorbed state the tetrameric structure
adopts a conformation which is slightly unfolded, as a consequence of
interaction between protein and BG surface.
with
without GA
before
Figure 3 DEER analysis of methemoglobin in solution before and after adsorption
on the bioactive glass without GA and with GA, with the resulting dipolar evolution
function (V(t), upper left inset), the form factor (F(t), upper right inset) as well as the
assumed Gaussian distance distribution P(r).
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