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.
Highlights
Life is regarded as a highly-organized precision structure made up of homochiral biomolecules
All proteinic amino acids can be resolved on cellulose thin layer chromatography at lower temperatures using development solvents such as n-butanol/pyridine/water or ethanol/pyridine/water
After the products for each saturation concentration of diammonium hydrogen phosphate were resolved on a column to obtain a chromatogram, tryptophanase activity on tryptophan synthesis was calculated from a peak area at a retention time of L-tryptophan on that chromatogram
Summary
Life is regarded as a highly-organized precision structure made up of homochiral biomolecules. Perhaps some elaborate contrivance is required to produce homochiral amino acid molecules enough to synthesize the polypeptide At least it should have a systematic mechanism with automatically developing chiral homogeneity [3], and should be a very sophisticated mechanism that selects and delivers the right enantiomeric type to the right place together with the exclusion of the opposite enantiomer to synthesize regularly-structured macromolecules. If early polypeptides were synthesized by spontaneous abiotic processes in a primitive racemic environment, the mechanism of homochirality may have already been incorporated into them, and their descendants may be traced to present enzymes Such mechanism is involved in enzyme stereospecificity in extant life. It becomes active toward D-tryptophan degradation in highly concentrated diammonium hydrogen phosphate solutions This reaction was discovered by sheer accident when we researched tryptophanase stereoselectivity. This paper reports D-serine reacts with tryptophanase as a substrate for L-tryptophan synthesis in the presence of diammonium hydrogen phosphate
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