Immunochemical studies on lens protein-protein complexes I. The heterogeneity and structure of complexed alpha-crystallin

A buffered extract of young cattle lenses filtered through Diaflo XM-300 membranes, retaining molecules above 300 000 daltons, was found to contain in the non-filterable fraction constituting 50% of soluble lens proteins α-and β-crystallins. The non-filterable fraction of soluble proteins from mature cattle lenses, constituting 87% of all crystallins, contained not only α- and β-crystallins, but γ-crystallins as well. Only α-crystallin, with a molecular weight above 300 000 daltons, was expected to remain in the non-filterable fraction. All of the β-crystallins, which have a molecular weight below 200 000 daltons, and γ-crystallins, with a molecular weight of about 20 000 daltons, if free in solution and not complexed, were expected to be in the filtrate.The lens proteins with a molecular weight above 300 000 daltons from young lens tissue were separated by gel chromatography (Bio-Rad A 15 m) into free α-crystallin followed by an α-β-crystallin complex. By the same procedure, the proteins above 300 000 daltons from mature lenses were separated into two complexes of quantitatively different α-β-γ-crystallin composition. A dependence of lens protein complex formation on the ionic composition of the solvent was observed. The differences between calf cortical and bovine nuclear complexes, found in buffer extracts, were much less pronounced in water extracts in which both contained γ-crystallins.Specific dissociation of the lens protein complexes was obtained by use of an anti-α-crystallin immunoadsorbent, as shown by the passage of the previously retained β- and γ-crystallins through a Diaflo XM-300 membrane. An anti-β-crystallin immunoadsorbent reacting with complexes from mature lens tissue yielded a non-filterable α-crystallin and a filterable γ-crystallin in the supernatant, indicating an absence of direct α-γ complexes. These results point to a potentially central role of β-crystallins in complex formation among lens proteins.