Accepted name: 2-methyl-6-phytyl-1,4-hydroquinone methyltransferase
Reaction: (1) S-adenosyl-L-methionine + 2-methyl-6-phytylbenzene-1,4-diol = S-adenosyl-L-homocysteine + 2,3-dimethyl-6-phytylbenzene-1,4-diol
(2) S-adenosyl-L-methionine + 2-methyl-6-all-trans-nonaprenylbenzene-1,4-diol = S-adenosyl-L-homocysteine + plastoquinol
(3) S-adenosyl-L-methionine + 6-geranylgeranyl-2-methylbenzene-1,4-diol = S-adenosyl-L-homocysteine + 6-geranylgeranyl-2,3-dimethylbenzene-1,4-diol
Other name(s): VTE3 (gene name); 2-methyl-6-solanyl-1,4-hydroquinone methyltransferase; MPBQ/MSBQ methyltransferase; MPBQ/MSBQ MT
Systematic name: S-adenosyl-L-methionine:2-methyl-6-phytyl-1,4-benzoquinol C-3-methyltransferase
Comments: Involved in the biosynthesis of plastoquinol, as well as vitamin E (tocopherols and tocotrienols).
1.  Shintani, D.K., Cheng, Z. and DellaPenna, D. The role of 2-methyl-6-phytylbenzoquinone methyltransferase in determining tocopherol composition in Synechocystis sp. PCC6803. FEBS Lett. 511 (2002) 1–5. [PMID: 11821038]
2.  Cheng, Z., Sattler, S., Maeda, H., Sakuragi, Y., Bryant, D.A. and DellaPenna, D. Highly divergent methyltransferases catalyze a conserved reaction in tocopherol and plastoquinone synthesis in cyanobacteria and photosynthetic eukaryotes. Plant Cell 15 (2003) 2343–2356. [PMID: 14508009]
3.  Van Eenennaam, A.L., Lincoln, K., Durrett, T.P., Valentin, H.E., Shewmaker, C.K., Thorne, G.M., Jiang, J., Baszis, S.R., Levering, C.K., Aasen, E.D., Hao, M., Stein, J.C., Norris, S.R. and Last, R.L. Engineering vitamin E content: from Arabidopsis mutant to soy oil. Plant Cell 15 (2003) 3007–3019. [PMID: 14630966]
[EC created 2014]
Accepted name: homogentisate phytyltransferase
Reaction: phytyl diphosphate + homogentisate = diphosphate + 2-methyl-6-phytylbenzene-1,4-diol + CO2
Glossary: 2-methyl-6-phytylbenzene-1,4-diol = MPBQ
Other name(s): HPT; VTE2 (gene name)
Systematic name: phytyl-diphosphate:homogentisate phytyltransferase
Comments: Requires Mg2+ for activity [3]. Involved in the biosynthesis of the vitamin E tocopherols. While the enzyme from the cyanobacterium Synechocystis PCC 6803 has an appreciable activity with geranylgeranyl diphosphate (EC, homogentisate geranylgeranyltransferase), the enzyme from the plant Arabidopsis thaliana has only a low activity with that substrate [1,3,4].
1.  Collakova, E. and DellaPenna, D. Isolation and functional analysis of homogentisate phytyltransferase from Synechocystis sp. PCC 6803 and Arabidopsis. Plant Physiol. 127 (2001) 1113–1124. [PMID: 11706191]
2.  Savidge, B., Weiss, J.D., Wong, Y.H., Lassner, M.W., Mitsky, T.A., Shewmaker, C.K., Post-Beittenmiller, D. and Valentin, H.E. Isolation and characterization of homogentisate phytyltransferase genes from Synechocystis sp. PCC 6803 and Arabidopsis. Plant Physiol. 129 (2002) 321–332. [PMID: 12011362]
3.  Sadre, R., Gruber, J. and Frentzen, M. Characterization of homogentisate prenyltransferases involved in plastoquinone-9 and tocochromanol biosynthesis. FEBS Lett. 580 (2006) 5357–5362. [PMID: 16989822]
4.  Yang, W., Cahoon, R.E., Hunter, S.C., Zhang, C., Han, J., Borgschulte, T. and Cahoon, E.B. Vitamin E biosynthesis: functional characterization of the monocot homogentisate geranylgeranyl transferase. Plant J. 65 (2011) 206–217. [PMID: 21223386]
[EC created 2014]
Accepted name: tocopherol cyclase
Reaction: (1) δ-tocopherol = 2-methyl-6-phytylbenzene-1,4-diol
(2) γ-tocopherol = 2,3-dimethyl-6-phytylbenzene-1,4-diol
(3) δ-tocotrienol = 6-geranylgeranyl-2-methylbenzene-1,4-diol
(4) γ-tocotrienol = 6-geranylgeranyl-2,3-dimethylbenzene-1,4-diol
Other name(s): VTE1 (gene name); SXD1 (gene name); δ/γ-tocopherol lyase (decyclizing)
Systematic name: δ/γ-tocopherol lyase (ring-opening)
Comments: The enzyme has been described from plants and cyanobacteria. It has similar activity with all four listed benzoquinol substrates. Involved in the biosynthesis of vitamin E (tocopherols and tocotrienols).
1.  Porfirova, S., Bergmuller, E., Tropf, S., Lemke, R. and Dormann, P. Isolation of an Arabidopsis mutant lacking vitamin E and identification of a cyclase essential for all tocopherol biosynthesis. Proc. Natl. Acad. Sci. USA 99 (2002) 12495–12500. [PMID: 12213958]
2.  Sattler, S.E., Cahoon, E.B., Coughlan, S.J. and DellaPenna, D. Characterization of tocopherol cyclases from higher plants and cyanobacteria. Evolutionary implications for tocopherol synthesis and function. Plant Physiol. 132 (2003) 2184–2195. [PMID: 12913173]
[EC created 2013]