Use of trinitrobenzensulfonate for affinity labeling of lysine residues at phosphate binding sites of some enzymes.

Trinitrobenzensulfonate, a reagent for lysine residues, inactivates lamb liver 6-phosphogluconate dehydrogenase through affinity labeling. Complete inactivation is due to the binding of only one residue of reagent per enzyme subunit. Other enzymes with a phosphate binding site are also inactivated by affinity labeling. It appears that trinitrobenzensulfonate, when used at low concentrations, first binds to a phosphate binding site, then reacts with a nearby lysine residue. This reagent presents some advantages over pyridoxal phosphate, which has similar characteristics.