Affinity and rate constants for interactions of bovine folate-binding protein and folate derivatives determined by optical biosensor technology. Effect of stereoselectivity

摘要

The interactions between bovine folate-binding protein (FBP) and different folate derivatives in pure diastereoisomeric forms were studied at pH 7.4 by a surface plasmon resonance technology (Biacore). The results show that folic acid had the most rapid association rate (k(a) = 1.0 x 10(6) M-1 s(-1)), whereas (6S)-5-HCO-5,6,7,8-tetrahydrofolic acid had the most rapid dissociation rate (k(d) = 3.2 X 10(-3) S-1). The equilibrium dissociation constant (K-D), calculated from the quotient of k(d)/k(a), showed that the two forms of folates not occurring in nature, that is, folic acid and (6R)-5-CH3-5,6,7,8-tetrahydrofolic acid, had the highest affinities for FBP, 20 and 160 pmol/L, respectively. The results thus show that there were great differences in the interactions between folate-binding protein and the major forms of folate derivatives. The nutritional implications of these differences are discussed.