Presqualene diphosphate synthase (, SSL-1 (gene)) is an enzyme with systematic name (2E,6E)-farnesyl-diphosphate:(2E,6E)-farnesyl-diphosphate farnesyltransferase (presqualene diphosphate forming). This enzyme catalyses the following chemical reaction
This enzyme is isolated from the green alga Botryococcus braunii BOT22.