G. R. Stark coauthored, with G. E. Davies, a 1970 experiment using protein cross-linking to investigate the organization of oligomeric proteins. The method connected a chemical intervention to a measurable series of protein subunit masses.[ref]
After reaction with dimethyl suberimidate, detergent gel electrophoresis separated individual chains and covalently linked combinations. The experiments included assemblies with identical subunits and assemblies containing different kinds of subunits; the latter showed unequal chemical reactivities.[ref]
The unequal-reactivity observation gives an important interpretive control. Failure to observe a linked pair need not mean that its members were far apart in the native protein: reactive groups may have been inaccessible or poorly reactive. Chemical proximity measurements must therefore be interpreted together with the chemistry used to record them.
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