ABSTRACT
The use of biological affinity to label amino acid residues at enzyme active sites, allosteric binding sites, substrate binding sites, and other types of binding sites on proteins has proved to be a powerful tool in the study of the relationship between structure and function. The concept of affinity labeling can be said to have been first advanced by S. J. Singer and co-workers. The reader is referred to J. C. Powers and co-workers, F. Wold, and B. V. Plapp for a more extensive consideration of the kinetics of interaction of affinity labels with proteins. There are at least three major considerations which must be satisfied in order to justify identification of a compound as a true affinity label. First, the reaction must show a rate saturation effect as one increases inhibitor concentration. Secondly, substrate, competitive inhibitor, or ligand must protect against modification and inactivation. Finally, the reaction must demonstrate stoichiometry with respect to sites modified/functional subunit.
