The environments ofTrp‐248 and Trp‐330 in tryptophan indole‐lyase from Escherichia coli

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Abstract
The two tryptophan residues, Trp‐248 and Trp‐330, in tryptophan indole‐lyase (tryptophanase) from E. coli have been separately mutated to phenylalanine using site‐directed mutagenesis. Both single tryptophan mutant enzymes have full catalytic activity, but exhibit different fluorescence and near‐UV circular dichroism spectra. These results indicate that Trp‐330 is more deeply buried than is Trp‐248, and is in a more asymmetric environment. Neither residue reacts with N‐bromosuccinimide (NBS), although tryptophan indole‐lyase is inactivated by NBS. These results demonstrate that the tryptophan residues in tryptophan indole‐lyase are not catalytically essential.