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2.1.1.295

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

For diagram of tocopherol biosynthesis, click here and for diagram of tocotrienol biosynthesis, click here

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).

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc

References:

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. [DOI] [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. [DOI] [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. [DOI] [PMID: 14630966]

[EC 2.1.1.295 created 2014]

2.5.1.116

Accepted name:

homogentisate geranylgeranyltransferase

Reaction:

geranylgeranyl diphosphate + homogentisate = diphosphate + 6-geranylgeranyl-2-methylbenzene-1,4-diol + CO₂

For diagram of the homogentisate pathways, click here

Glossary:

6-geranylgeranyl-2-methylbenzene-1,4-diol = MGGBQ

Other name(s):

HGGT; slr1736 (gene name)

Systematic name:

geranylgeranyl-diphosphate:homogentisate geranylgeranyltransferase

Comments:

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].

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc

References:

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.	Cahoon, E.B., Hall, S.E., Ripp, K.G., Ganzke, T.S., Hitz, W.D. and Coughlan, S.J. Metabolic redesign of vitamin E biosynthesis in plants for tocotrienol production and increased antioxidant content. Nat. Biotechnol. 21 (2003) 1082–1087. [DOI] [PMID: 12897790]
3.	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. [DOI] [PMID: 21223386]

[EC 2.5.1.116 created 2014]

5.5.1.24

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

For diagram of tocopherol biosynthesis, click here and for diagram of tocotrienol biosynthesis, click here

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).

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc

References:

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. [DOI] [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. [DOI] [PMID: 12913173]

[EC 5.5.1.24 created 2013]