Photoaffinity reagents biological activity

The investigator should be aware of a few possible pitfalls in binding studies and other assays. First, the reagent should be pure. This is of the utmost importance if the photoaffinity label is a derivative of the natural ligand and turns out to be less potent in its biological activity. In numerous cases where a derivative has appeared to be (say one hundred times) less active than its precursor, it has not been shown that the precursor was not a contaminant (say 1 %) of the derivative which was actually completely... 

In this regard, implicit in the use of affinity labels for the modification of proteins is that all experiments should be attempted under conditions where the protein is biologically active and binds its specific ligands and/or substrates. Incubation of the affinity label with the protein under any other conditions may provide misleading information that will undermine the inherent information content of the technique. In all cases of affinity and photoaffinity labels which have been cited in this monograph, the protein has been incubated with the modification reagent under conditions of temperature, pH and ionic strength where the macromoiecule was stable and active. 

The availability of the described photoaffinity reagents represent chemical tools for the examination of the ligand binding regions of a wide variety of biologically active systems. 

M. Dias, R. Momet, M. Laloue, Synthesis, azido-tetrazole equihbrium studies and biological activity of l-(2-azido-6-chloropyrid-4-yl)-3-phenylimea, a photoaffinity labeling reagent for cytokinin-binding proteins, Bioorg. Med Chem., 1995, 5,361-366. 

---