1.3.1.96 additional information squalene and botryococcene are branched-chain, triterpene compounds that arise from the head-tohead condensation of two molecules of farnesyl diphosphate to yield 1'-1 and 1'-3 linkages, respectively. Different enzymes are responsible for botryococcene and squalene biosynthesis in the green alga Botryococcus braunii race B. The specificity for the 1'-1 and 1'-3 linkages is controlled by residues in the active sites that can mediate catalytic specificity. Identification of several amino acid positions contributing to the rearrangement of the cyclopropyl intermediate to squalene, The same positions do not appear to be sufficient to account for the cyclopropyl rearrangement to give botryococcene, oerview 1.3.1.96 presqualene diphosphate + NADPH + H+ -