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Tryptophanase-Catalyzed L-Tryptophan Synthesis from D-Serine in the Presence of Diammonium Hydrogen Phosphate
Sustainable Environmental Studies, Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan
* Author to whom correspondence should be addressed.
Received: 21 May 2009; Accepted: 1 June 2009 / Published: 3 June 2009
Abstract: Tryptophanase, an enzyme with extreme absolute stereospecificity for optically active stereoisomers, catalyzes the synthesis of L-tryptophan from L-serine and indole through a β-substitution mechanism of the ping-pong type, and has no activity on D-serine. We previously reported that tryptophanase changed its stereospecificity to degrade D-tryptophan in highly concentrated diammonium hydrogen phosphate, (NH4)2HPO4 solution. The present study provided the same stereospecific change seen in the D-tryptophan degradation reaction also occurs in tryptophan synthesis from D-serine. Tryptophanase became active to D-serine to synthesize L-tryptophan in the presence of diammonium hydrogen phosphate. This reaction has never been reported before. D-serine seems to undergo β-replacement via an enzyme-bonded α-aminoacylate intermediate to yield L-tryptophan.
Keywords: tryptophanase; diammonium hydrogen phosphate; D-serine; tryptophan synthesis; stereospecific change
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MDPI and ACS Style
Shimada, A.; Ozaki, H.; Saito, T.; Noriko, F. Tryptophanase-Catalyzed L-Tryptophan Synthesis from D-Serine in the Presence of Diammonium Hydrogen Phosphate. Int. J. Mol. Sci. 2009, 10, 2578-2590.
Shimada A, Ozaki H, Saito T, Noriko F. Tryptophanase-Catalyzed L-Tryptophan Synthesis from D-Serine in the Presence of Diammonium Hydrogen Phosphate. International Journal of Molecular Sciences. 2009; 10(6):2578-2590.
Shimada, Akihiko; Ozaki, Haruka; Saito, Takeshi; Noriko, Fujii. 2009. "Tryptophanase-Catalyzed L-Tryptophan Synthesis from D-Serine in the Presence of Diammonium Hydrogen Phosphate." Int. J. Mol. Sci. 10, no. 6: 2578-2590.