MetaCyc Enzyme: tryptophan synthase

Gene: TSBType2 Accession Number: AT5G38530 (MetaCyc)

Species: Arabidopsis thaliana col

Subunit composition of tryptophan synthase = [TSBType2]2
         trytophan synthase, beta subunit = TSBType2

TSBType2 is a tryptophan synthase, beta subunit (TSB) (type 2) enzyme that catalyzes the condensation of serine and indole to form tryptophan in vitro [Yin10]. Although there are several other TSB enzymes in Arabidopsis, including TSB1, they belong to the type 1 portion of the enzyme family. Land plants as far back as mosses at least, have had members of both types of TSBs present in their genomes. In most organs, TSBtype2 is transcripts are expressed at a lower level than TSB1but in dry seeds they are expressed at comparable levels [Yin10].

This enzyme has a remarkably low Km of 74 +/- 12 nM for indole, but it has a much higher Km of 35 mM for L-serine. No serine deaminase activity has been observed for the TSBType2 enzyme in vitro [Yin10].

Size exclusion chromatography indicates that this protein purifies at a weight that is consistent with it forming a homodimer, similar to other microbial type 2 TSB enzymes that have been previously characterized [Yin10].

Its biological role has not yet been determined, but it has a very high affinity for indole which may be involved in allowing TSBtype2 to carefully limit free indole build-up. But, to date no overall change in plant morphology or seedling root growth have been observed in tsbtype2 mutants, indicating that this gene is not essential under optimum conditions [Yin10].

Molecular Weight of Multimer: 90.0 kD (experimental) [Yin10]

Unification Links: PhylomeDB:Q9FFW8, Pride:Q9FFW8, Protein Model Portal:Q9FFW8, SMR:Q9FFW8, String:3702.AT5G38530.1, TAIR:AT5G38530, UniProt:Q9FFW8

Relationship Links: InterPro:IN-FAMILY:IPR001926, InterPro:IN-FAMILY:IPR006316, InterPro:IN-FAMILY:IPR023026, Panther:IN-FAMILY:PTHR10314:SF21, Pfam:IN-FAMILY:PF00291

Gene-Reaction Schematic

Gene-Reaction Schematic

Created 13-Apr-2011 by Dreher KA, TAIR

Enzymatic reaction of: tryptophan synthase

Inferred from experiment

EC Number:

L-serine + indole → L-tryptophan + H2O

The direction shown, i.e. which substrates are on the left and right sides, is in accordance with the Enzyme Commission system.

The reaction is favored in the direction shown.

In Pathways: L-tryptophan biosynthesis

The kcat of the reaction measured using indole is 7.0 +/- 0.3 x 10-3 s-1. The kcat of the reaction measured using serine is 15.5 +/- 0.9 x 10-3 s-1 [Yin10] .

Kinetic Parameters:
Substrate Km (μM) Citations
indole 0.074 [Yin10]
L-serine 35000.0 [Yin10]


Yin10: Yin R, Frey M, Gierl A, Glawischnig E (2010). "Plants contain two distinct classes of functional tryptophan synthase beta proteins." Phytochemistry 71(14-15);1667-72. PMID: 20701934

Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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