Conformation digestive system

These footprinting analyses, based on enzymic and chemical digestion, are now widely used to define DNA (and RNA) and their complexes with various ligands. Recently active radical probes have been used as footprinting agents in protection assays in a variety of systems (e.g., Tullius and Dombroski, 1986 Chalepakis and Beato, 1989 Hayes and Tullius, 1989 Schickor et al., 1990). Such probes rely on active radical intermediates, most likely hydroxyl radicals, released by Fe(II) in the presence of an electron donor, probably via a Fenton reaction. In addition, hydroxyl radicals also appear to react with DNA in a conformation-specific manner which may allow some prediction of DNA secondary structure (see Burkhoft and Tullius, 1987 Zorbas et al., 1989 Lu et al., 1990). 

It is well known that the specific scission of one or a few peptide bonds in a precursor protein is required for activation of several digestive enzymes (15), the enzymes of the blood clotting system (16), complement action (17), and insulin (18), as well as others. In some cases, conformational changes occur following peptide bond scission to form the specific active site. 

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