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Binding of Oxovanadium(IV) Complexes to Blood Serum Albumins
In this work the binding of VIVO2+ and VIVO-complexes to
serum albumins {human serum albumin (HSA), bovine serum albumin
(BSA) and porcine serum albumin (PSA)} are studied using circular
dichroism (CD), electron paramagnetic resonance (EPR) and visible
absorption spectroscopy. The results confirm previous findings that
VIVO2+ occupies at least two types of binding sites on albumin: ‘the
strong vanadium binding site’ (designated by VBS1) and ‘the weak
vanadium binding sites’ (designated by VBS2). VBS1 binds 1 mol
equivalent of VIVO2+. On the other hand VBS2 correspond to binding
of several mol equivalents of VIVO, and studies done with PSA in the
presence of excess ZnII ions indicate that VSB2 corresponds to two
distinct types of sites. The hyperfine coupling constant Az for VIVO2+
binding at VBS2 on HSA and BSA are all very similar (~168 × 10-4
cm-1) but differ slightly on PSA (~166 × 10-4 cm-1) due to differences
in the binding sets. When (VIVO)-HSA systems are titrated with maltol
ternary species of (maltol)m(VIVO)mHSA and (maltol)2m(VIVO)mHSA
stoichiometry form which are clearly distinguishable from the binary
(VIVO)-HSA system by the type and intensity of the CD spectra
recorded. Changes are also observable in the intensity of the X-band
EPR spectra, but not much in the hyperfine coupling constants Az,
which are all in the range 166-167 × 10-4 cm-1. The results further
demonstrate that the presence of maltol may enhance the binding of
VIVO to albumin
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