Human glucosephosphate isomerase was subjected to a series of chemical modifications aimed at identifying residues essential for catalytic activity. Specific lysyl, arginyl, tryptophanyl and histidyl residues were found to react stoichiometrically with pyridoxal-5'-phosphate-NaBH4, 2,3-butadione, N-bromosuccinimide and N-bromoacetylethanolamine phosphate, respectively
