PH-INDUCED REVERSIBLE DISSOCIATION OF TETRAMERIC DUCK LENS DELTA-CRYSTALLIN

Animal lenses constitute many soluble proteins, which play a prominent role in eyes' light transparency. delta 2-Crystallin, one of the majo r taxon-specific crystallins in duck lens, is a tetrameric protein con sisting of four identical subunits, which contain endogenous argininos uccinate lyase activity. Under a neutral pH environment in this work, the protein was cross-linked with glutaraldehyde as tetrameric and dim eric forms with tetramer as the major form. Under acidic conditions, t he protein was time-dependently dissociated into monomers with amino a cid residues of pK(a) values 6.29+/-0.45 and 7.17+/-0.49 being involve d in the monomer-monomer interactions and 6.20+/-0.10 and 8.88+/-0.07 in the dimer-dimer interactions. Duck lens delta 2-crystallin thus pos sesses a double dimer structure (alpha(2))(2) with stronger monomer-mo nomer interactions than the dimer-dimer interactions. The acidic prote in solution's reneutralization caused rapid reassociation of monomers into dimers and tetramers. The tetramer-dimer-monomer dissociation-rea ssociation thus is a pH-dependent freely interconvertible process. (C) 1997 Academic Press Limited.