Dimer-tetramer and monomer-dimer-tetramer equilibria of tetrameric hemoglobins and their single chains in the CO form, respectively, were evaluated using the microbatch multiangle light-scattering (MALS) analysis system. The molecular weights of human Hb A and Hb F in the CO form were dependent on concentration. The dissociation constants to dimers of Hb A and Hb F were 2.58 X 10(-6) and 0.66 x 10(-6), respectively. Equilibration of single globin chains, including alpha, beta, and gamma chains, was also evaluated by the same method. The dissociation constants of a-chain dimers to monomers, of beta-chain tetramers to monomers, and of gamma-chain tetramers to dimers were 14 x 10(-6). 25 x 10(-17), and 6.86 X 10(-6) M, respectively. These results indicate that the MALS analysis system can not only determine molecular weight but also characterize protein-protein interactions of multi-subunit proteins. (C) 2002 Elsevier Science (USA).