Hydrophobic interactions are the prevalent force in bromelain:Fab′ complex

Antibromelain polyclonal antibodies against stem bromelain were raised in male albino rabbits and the Fab' monomers isolated from the IgG of the immune sera as reported in our earlier communication (Gupta, P., Khan, R. H., and Saleemuddin, M. (2003) Biochim. Biophys. Acta, 1646, 131-135). Further, as evident from that communication, bromelain:Fab' complex has 1 : 1 stoichiometry. The stability of bromelain:Fab' complex (1 : 1) was investigated by far and near-UV CD and fluorescence measurements. Addition of up to 1.8 M NaCl caused no significant changes in fluorescence signals and near-UV CD peak pattern. However, the spectral studies together with gel filtration studies suggest dissociation of the complex beyond 5% (v/v) methanol. These results show that hydrophobic interactions play a pronounced role in the binding of Fab' to bromelain while electrostatic interactions may be less crucial.