Studies on enzyme activities for useful isoprenoid biosynthesis in a microalga.

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Green microalga Botryococcus braunii produces a large amount of liquid hydrocarbons that are promising as a renewable energy source. This alga is classified into three chemical races A, B, and L by the type of hydrocarbon produced. Among the three, the B race that produces triterpenoid such as botryococcenes and squalene derivatives is the most promising as a renewable energy source. Botryococcene is thought to be synthesized by condensation of two molecules of farnesyl diphosphate by a squalene synthase-like enzyme. A cDNA clone very similar to squalene synthase gene was isolated from a cDNA library and was expressed in E.coli. The gene product did not show either squalene synthase activity or botryococcene activity, but enhanced endogenous botryococcene synthase activity in the algal cell homogenate. Some factors such as galactose or sodium chloride enhanced botryococcene synthase activity. The enhancement of enzyme activity by the gene product was not seen when it was mixed with heat-treated algal homogenate. Thus something like a protein that is unstable to heat is concerning to the expression of the enzyme activity.