BINDING OF FANTOFARONE, A NOVEL CA2-ALBUMIN - A FLUORESCENCE STUDY( ANTAGONIST, TO SERUM)

Using the fluorescent properties of fantofarone, we have studied the i nteractions between this novel calcium entry blocker and human and bov ine serum albumins. Binding of fantofarone, which is poorly fluorescen t in aqueous buffer, resulted in a large increase in the fluorescent s ignal (lambda(ex) = 335 nm, lambda(em) = 395 nm). Fantofarone bound to a single site with a dissociation constant (K-d) of 11-12 X 10(-6) M. The number of sites and the K-d value were not modified by either NaC l (134 mM) or Ca2+ (10 mM). Two values of fluorescence lifetime (tau(1 ) = 12.8 ns and tau(2) = 3.5 nS) with respective fractional contributi ons (chi(1) = 0.79 and chi(2) = 0.21) were determined. Quenching by io dide resulted in a downward curved Stern-Volmer plot, where 36% of the fluorescence was quenched with a quenching constant (K-Q) of 11.4 M(- 1), From the measured degree of fluorescence depolarization and fluore scence lifetime, a value of rotational relaxation time of 109 ns was c alculated.