Photolytically derived carbenes were first used by Westheimer's group (1) as labeling agents for proteins. The carbenes and the related nitrenes (2) are useful agents for labeling receptor sites on proteins where a primary, non-covalent complex can be formed between protein and label. Such complexes can subsequently be triggered by near-UV light to give a carbene or nitrene capable of reacting covalently with amino acid side chains. Diazoketone reagents have been used with myeloma proteins and antibodies (3, 4) and supplement the information given by other types of affinity reagents labeling residues present at or near the combining site (5–7).

A γA myeloma protein (protein 460) derived from the mouse tumor line MOPC 460 binds menadione with a K° in the order of 104l/mol. This myeloma protein also binds other haptens with higher binding constants elsewhere in the combining region (8). We have used an affinity label derived from menadione to study the primary and three-dimensional structure of immunoglobulin-combining sites.

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