The Quaternary Structure of Bovine α‐Crystallin

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Abstract
Reaction of calf .alpha.-crystallin, a major structural lens protein which consists of .apprx. 30 A and 10 B subunits, with various bisimido esters at pH 8.0-8.5 and room temperature, leads to inter-subunit crosslinking. Little difference occurs in the efficiency of crosslinking by reagents of a homologous series with different lengths (from C6-C12). At any stage of the reaction an exponential decrease is found in the amounts of crosslinked dimer, trimer, tetramer ect., with no preference for the formation of any particular oligomer. All subunits on the surface of the spherical .alpha.-crystallin molecule apparently are in quasiequivalent positions. MW analysis by dodecylsulfate gel electrophoresis and reversible crosslinking show that A and B subunits occur in an apparently constant ratio in the crosslinked oligomers. Both types of subunits apparently are randomly arranged on the surface of the .alpha.-crystallin molecule. Not all of the subunits can form inter-chain crosslinks, as a limiting value of .apprx. 60% of the subunits is found in oligomeric form. A core of subunits which is inaccessible to certain chemical reagents may exist, although other alternatives are discussed.