Role of the tryptophan group in the action of pullulanase of Aerobacter aerogenes.

1. Pullulanase [EC 3.2.1.4.] was inhibited by Hg2+, N-bromosuccinimide, 2-hydroxy-5-nitrobenzyl bromide, riboflavine 5'-phosphate, histamine, imidazole, and carbodiimide. 2. The tryptophan groups of the pullulanase were modified by N-bromosuccinimede. It was found that one or two of the 25 tryptophan groups seemed to be important for the activity. 3. Studies on difference spectra using various substrates suggested that the tryptophan groups were important for the formation of an enzyme-substrate complex.