Binding equilibrium study between Mn(II) and HSA or BSA

The binding of Mn( II:) to human serum albumin (HSA) or bovine serum albumi n (BSA) has been studied by equilibrium dialysis at physiological pH (7.43) . The Scatchard analysis indicates that there are 1.8 and 1.9 strong bindin g sites of Mn( Il) in HSA and BSA, respectively. The successive stability c onstants which are reported for the first time are obtained by non-linear l east-squares methods fitting Bjerrum formula. For both Mn( Il)-HSA and Mn(I I)-BSA systems, the order of magnitude of K-1 was found to be 10(4). The an alyses of Hill plots and free energy coupling show that the positive cooper ative effect was found in both Mn( II)-HSA and Mn( Il)-BSA systems. The res ults of Mn ( Il) competing with Cu (II). zn( II), Cd(II) or Ca(I) to bind t o HSA or BSA further support the conjecture that there are two strong bindi ng sites of Mn( II:) in both HSA and BSA. One is most probably located at t he tripeptide segment of N-terminal sequence of HSA and BSA molecules invol ving four groups composed of nitrogen atoms, and the fifth coordination ato m is the carboxyl oxygen of Asp(1). The coordinated atoms of the other are most probably almost all oxygen atoms.