Reaction of indole and analogues with amino acid complexes of Escherichia coli tryptophan indole-lyase: detection of a new reaction intermediate by rapid-scanning stopped-flow spectrophotometry.
The effects of indole and analogues on the reaction of Escherichia coli tryptophan indole-lyase (tryptophanase) with amino acid substrates and quasisubstrates have been studied by rapid-scanning and single-wavelength stopped-flow spectrophotometry. Indole binds rapidly (within the dead time of the stopped-flow instrument) to both the external aldimine and quinonoid complexes with L-alanine, and the absorbance of the quinonoid intermediate decreases in a subsequent slow relaxation. Indoline binds preferentially to the external aldimine complex with L-alanine, while benzimidazole binds selectively to the quinonoid complex of L-alanine. Indole and indoline do not significantly affect the spectrum of the quinonoid intermediates formed in the reaction of the enzyme with S-alkyl-L-cysteines, but benzimidazole causes a rapid decrease in the quinonoid peak at 512 nm and the appearance of a new peak at 345 nm. Benzimidazole also causes a rapid decrease in the quinonoid peak at 505 nm formed in the reaction with L-tryptophan and the appearance of a new absorbance peak at 345 nm. Furthermore, addition of benzimidazole to solutions of enzyme, potassium pyruvate, and ammonium chloride results in the formation of a similar absorption peak at 340 nm. This complex reacts rapidly with indole to form a quinonoid intermediate very similar to that formed from L-tryptophan. This new intermediate is formed faster than catalytic turnover (kcat = 6.8 s-1) and may be an alpha-aminoacrylate intermediate bound as a gem-diamine.
Phillips
R S
RS
Department of Chemistry, School of Chemical Sciences, University of Georgia, Athens 30602.
D000596:Amino Acids / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D007211:Indoles / Q000494:pharmacology*; D007700:Kinetics; D008433:Mathematics; D008962:Models, Theoretical; D011485:Protein Binding; D013053:Spectrophotometry / Q000379:methods; D013997:Time Factors; D014364:Tryptophan / Q000378:metabolism; D014368:Tryptophanase / Q000378:metabolism*
D000596:Amino Acids; D007211:Indoles; C030374:indole; D014364:Tryptophan; D014368:Tryptophanase