Requires Mg2+ for activity. Involved in the biosynthesis of the vitamin E, tocotrienols. While the enzyme from the bacterium Synechocystis PCC 6803 has higher activity with phytyl diphosphate (EC 2.5.1.115, homogentisate phytyltransferase), the enzymes from barley, rice and wheat have only a low activity with that substrate [2].