. "Catalysis of the reaction: 2 farnesyl diphosphate = diphosphate + presqualene diphosphate." . . "farnesyl-diphosphate farnesyltransferase activity" . "farnesyl-diphosphate:farnesyl-diphosphate farnesyltransferase activity" . "presqualene synthase activity" . "presqualene-diphosphate synthase activity" . . .