Isolated from the green alga Botryococcus braunii BOT22. Unlike EC 2.5.1.21, squalene synthase, where squalene is formed in one step from farnesyl diphosphate, in this alga the intermediate presqualene diphosphate is generated and released by this enzyme. This compound is then converted into either squalene (by EC 1.3.1.96, Botryococcus squalene synthase) or botryococcene (EC 1.3.1.97, botryococcene synthase).