Interaction mechanism between indoxyl sulfate, a typical uremic toxin bound to site II, and ligands bound to site I of human serum albumin.
OBJECTIVE
The study was performed for clarifying the mechanism of interaction between indoxyl sulfate (IS), a typical uremic toxin bound to site II, and site I-ligands when bound to human serum albumin (HSA). The effect of the N to B transition on the interactions was also examined.


METHODS
Quantitative investigation of the relations between ligands bound to HSA was performed by equilibrium dialysis, and the binding data were analyzed on the basis of a theoretical model for simultaneous binding of two ligands.


RESULTS
The high-affinity binding constants for the site I-ligands warfarin (WF) and dansyl-L-asparagine (DNSA) increased with increasing pH, whereas those for the site II-ligands IS and dansylsarcosine (DNSS) were hardly affected by pH. Mutual displacement experiments showed that even though IS binds to site II it influenced binding of DNSA at the azapropazone binding area in site I. By contrast, it is unlikely that IS affects the WF binding area of site I. Furthermore, pH-profiles showed that the interaction between IS and DNSA was very sensitive to the N to B transition: "competitive-like" strong allosteric regulation was observed for binding of the two ligands to the N conformer (pH 6.5), whereas in the B conformation (pH 8.5) binding of these molecules was nearly "independent".


CONCLUSIONS
The present data provide useful information for elucidating a potential mechanism of interaction between drugs and endogenous substances including uremic toxins.
Sakai
T
T
Faculty of Pharmaceutical Sciences, Kumamoto University, Japan.
Yamasaki
K
K
Sako
T
T
Kragh-Hansen
U
U
Suenaga
A
A
Otagiri
M
M
D000925:Anticoagulants / Q000493:pharmacokinetics; D001216:Asparagine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D001665:Binding Sites / Q000502:physiology; D003619:Dansyl Compounds / Q000493:pharmacokinetics; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007200:Indican / Q000493:pharmacokinetics*; D008024:Ligands; D012709:Serum Albumin / Q000378:metabolism*; D014118:Toxins, Biological / Q000493:pharmacokinetics*; D014511:Uremia / Q000378:metabolism*; D014859:Warfarin / Q000493:pharmacokinetics
D000925:Anticoagulants; D003619:Dansyl Compounds; D005456:Fluorescent Dyes; D008024:Ligands; D012709:Serum Albumin; D014118:Toxins, Biological; C031592:dansyl asparagine; D014859:Warfarin; D001216:Asparagine; D007200:Indican