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

绿色微藻布朗氏bottryococcus braunii可生产大量液态烃，作为一种可再生能源具有广阔的前景。根据产生的碳氢化合物类型，这种藻类可分为A、B和L三个化学人种。其中，产三萜如芽孢杆菌和角鲨烯衍生物的B小种是最有前途的可再生能源。芽孢杆菌被认为是由角鲨烯合成酶样酶将两个二磷酸法尼酯分子缩合而成的。从cDNA文库中分离到一个与角鲨烯合成酶基因非常相似的cDNA克隆，并在大肠杆菌中表达。该基因产物既不具有角鲨烯合成酶活性，也不具有生芽孢菌合成酶活性，但在藻细胞均浆中增强了内源性生芽孢菌合成酶活性。半乳糖或氯化钠等因素可增强芽孢杆菌合成酶活性。该基因产物与经过热处理的海藻匀浆混合后，酶活性未见明显增强。因此，对热不稳定的蛋白质之类的东西与酶活性的表达有关。

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.