Ketoprofen (KP),
which causes photosensitivity by interacting with
serum albumin (SA), and three drugs, ibuprofen (IBP), naproxen (NPX),
and diazepam (DZP), which share the same binding site, were investigated
for their interaction with bovine SA (BSA). For KP, DZP, and IBP,
where drug-concentration-dependent quenching of BSA-intrinsic fluorescence
was observed, a modified Stern–Volmer plot showed that dynamic
quenching was dominant for KP and static quenching was dominant for
DZP and IBP. However, this alone cannot be compared with NPX. Therefore,
by performing singular value decomposition (SVD) fluorescence spectroscopy,
we were able to find the behavior of the drug-concentration-dependent
Langmuir-type principal component vectors.KSVDobtained by the Langmuir equation showed a high correlation
with the static extinction constantV. Therefore,KSVDindicates the association constant of the
drug with BSA and it was found that NPX and IBP had higher values
than KP. Finally, in the analysis of the temperature factors of amino
acid residues in each drug-binding region and Trp residues, KP and
NPX significantly reduced these temperature factors whereas DZP and
IBP hardly changed them. This result is consistent with the dynamic
and static quenching dominance in the total quenching mechanism. Summarizing
the results so far, it was shown that penetration into the hydrophobic
core inside BSA can be achieved not only by one of the multiple aromatic
rings and propionic acid groups but also by the joint effect of both.
In this study, SVD enabled us to extract information on drug adsorption
to BSA from fluorescence spectra. Furthermore, the application of
SVD is expected to make it possible to perform fluorescence analysis
for drug binding to proteins without being limited by the fluorescence
properties of the drug.