INTERACTION OF MYOINOSITOL HEXAPHOSPHATE (MIHP) WITH BETA-GLOBULIN FROM SESAMUM-INDICUM L - KINETICS AND THERMODYNAMICS

Beta-Globulin, the low molecular weight protein fraction from Sesamum indicum L., interacts with myo-inositol hexaphosphate (MIHP) maximally at pH 3.0, with concomitant precipitation up to 85 +/- 2% at an MIHP concentration of 8 x 10(-4) m. The kinetics of interaction as followed by stopped-flow spectrophotometry suggested the reaction to be of pse udo first-order, having an initial fast step followed by a relatively slow step of rate constants 1.9 x 10(-2) s-1 and 1.2 x 10(-3) s-1 , re spectively at 1 X 10(-4) M MIHP concentration. The analysis of the com plex indicated the presence of polymer as seen in sedimentation veloci ty experiment. This was accompanied by conformational change of a thre e-fold decrease in beta-structure and also an increase in fluorescence emission intensity accompanied with a red shift from 330 to 334 nm. S toichiometric analysis of MIHP binding suggested four independent bind ing sites for MIHP, with a free energy change, DELTAG(o) = -5.1 kcal m ol-1 resulting from a binding constant of 3.6 x 10(3) M-1. (C) Munksga ard 1993.