Journal of Lipid Research, Vol 25, 1177-1183, Copyright © 1984 by Lipid Research, Inc.
Evidence for a common high affinity binding site on glutathione S- transferase B for lithocholic acid and bilirubin
Y Sugiyama, A Stolz, M Sugimoto and N Kaplowitz
Binding of lithocholic acid, bilirubin, and gossypol to glutathione S-
transferase B (ligandin or transferase YaYc) was compared using four
methods. Tryptophan quenching revealed a single high affinity site for
bilirubin and gossypol but could not be used for lithocholic acid. Both
displacement of the fluorescent probe, 1-anilino-8- naphthalenesulfonate,
and spectral changes induced by bilirubin binding demonstrated a common
high affinity site for which all three ligands compete. Similar results
were obtained by equilibrium dialysis. The dissociation constants for the
binding of both bilirubin and lithocholic acid were comparable with the
various methods (range 0.2- 0.7 microM). Thus, lithocholic acid and
bilirubin share a high affinity binding site on gluthathione S-transferase
B that appears to be separate from the binding site for substrates.