|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 [Sharkey08]).
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].
Enzymatic reaction of: isoprene synthase
EC Number: 18.104.22.168
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.
T(opt): 40 °C [Sasaki05]
pH(opt): 8.0 [Sasaki05]
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