Studies on enzymes concerned in the biosynthesis of large amounts of useful isoprenoids by a green microalga

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A 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. The B race produces a large amount of triterpene hydrocarbons. All terpenes are biosynthesized from the universal precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). The triterpenes produced by the alga are specifically synthesized by precursors derived from not the mevalonate pathway but the "non-mevalonate (DOXP/MEP)" pathway. We tried to isolate cDNA clone of 1-deoxy-D-xylulose 5-phosphate synthase (DXS) that catalyzes the first reaction in the DOXP/MEP pathway. in order to understand the mechanism of hydrocarbon production by B. braunii, and obtained three different clones All of these genes coded active DXS proteins. Kinetic parameters of the recombinant DXS proteins from this alga were not significantly different from those of the higher plants. Levels of mRNA for three DXS were high when the alga actively produces triterpenes.