MetaCyc Enzyme: isoprene synthase

Gene: IspS Accession Number: G-11347 (MetaCyc)

Synonyms: isoprene synthase

Species: Populus alba

Isoprene synthase is the final enzyme in the isoprene biosynthesis pathway. As such, it is a key regulator of isoprene emissions from plants (rev in [Sharkey08a]).

This enzyme has a transit peptide that is capable of targeting GFP to chloroplasts, suggesting that the native enzyme is present in that organelle [Sasaki05]. When a truncated form of isoprene synthase lacking the transit peptide is expressed in vitro it synthesizes isoprene [Sasaki05]. The Km of the enzyme for DMAPP is quite high, but the value is similar for an isoprene synthase studied in P.tremuloides [Silver95]. Both enzymes appear to be Mg2+-dependent, but this enzyme can also show reduced activity (~20-30%) with Mn2+ and Co2+ in vitro [Sasaki05].

IspS transcript levels are up-regulated in response to both heat (40 deg C) and continuous light whereas they are down-regulated in the dark [Sasaki05]. Not surprisingly based on its expression pattern, this enzyme has a relatively high temperature optimum [Sasaki05]. In addition, this gene appears to expressed at much higher levels in leaves than in stems and roots in accordance with the observed isoprene emission from leaves [Sasaki05].

Unification Links: Entrez-Nucleotide:AB198180 , Entrez:BAD98243 , Protein Model Portal:Q50L36 , UniProt:Q50L36

Relationship Links: InterPro:IN-FAMILY:IPR001906 , InterPro:IN-FAMILY:IPR005630 , InterPro:IN-FAMILY:IPR008930 , InterPro:IN-FAMILY:IPR008949 , Pfam:IN-FAMILY:PF01397 , Pfam:IN-FAMILY:PF03936

Gene-Reaction Schematic: ?

Gene-Reaction Schematic


Created 05-Jun-2009 by Dreher KA , TAIR

Enzymatic reaction of: isoprene synthase

EC Number:

dimethylallyl diphosphate <=> isoprene + diphosphate

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

In Pathways: isoprene biosynthesis I , isoprene biosynthesis II (engineered)

Cofactors or Prosthetic Groups: Mg2+ [Sasaki05]

Kinetic Parameters:

Km (μM)
dimethylallyl diphosphate

T(opt): 40 °C [Sasaki05]

pH(opt): 8.0 [Sasaki05]


Sasaki05: Sasaki K, Ohara K, Yazaki K (2005). "Gene expression and characterization of isoprene synthase from Populus alba." FEBS Lett 579(11);2514-8. PMID: 15848197

Sharkey08a: Sharkey TD, Wiberley AE, Donohue AR (2008). "Isoprene emission from plants: why and how." Ann Bot (Lond) 101(1);5-18. PMID: 17921528

Silver95: Silver GM, Fall R (1995). "Characterization of aspen isoprene synthase, an enzyme responsible for leaf isoprene emission to the atmosphere." J Biol Chem 270(22);13010-6. PMID: 7768893

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 19.0 on Wed Oct 7, 2015, biocyc14.