To characterize the interaction between EIIAgnt and EIIBgnt, isothermal titration calorimetry (ITC) experiments were performed using recombinantly expressed proteins. The thermodynamic parameters of the complex formation reaction are summarized in Table 2. For the association constant KA a value of 108 M?1 (37 °C) was determined which reflects a strong interaction between the two components and shows that the proteins are almost entirely present as a complex in the equilibrium. This finding is in Doxorubicin to the significantly weaker interactions reported for other EIIA:EIIB systems (KD values of 3.7 mM for the mannitol [23], 0.5 mM for the mannose [6] and 14 μM for the galactitol PTS systems from E. coli [24]). Although the reasons for such an unusually strong affinity remain to be elucidated radioisotope may be hypothesized, that in systems in which EIIA and EIIB are present on separate polypeptide chains (as, e.g., for the gluconate or the galactitol system) higher affinities are required compared to systems in which EIIA and EIIB are located on a single polypeptide chain.