Fig 1. Biosynthesis and metabolism of triterpenes in Botryococcus braunii, race B.

Squalene synthase (SS) converts two molecules of farnesyl pyrophosphate (FPP) into one molecule of squalene via presqualene pyrophosphate (PSPP). Squalene synthase-like protein (SSL) -1 (SSL-1) catalyzes formation of PSPP from two FPPs, SSL-2 converts PSPP into squalene, and SSL-3 synthesizes C₃₀ botryococcene from PSPP. Squalene and C₃₀ botryococcene are methylated and excreted outside cells as free hydrocarbons that can be used as biofuels. Squalene is epoxidized into squalene 2,3-epoxide that is the precursor of membrane sterols or into squalene 10,11-epoxide that is further converted into hydrophobic secondary metabolites including biopolymers.