The Enzyme Database

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EC 2.1.1.115     
Accepted name: (RS)-1-benzyl-1,2,3,4-tetrahydroisoquinoline N-methyltransferase
Reaction: S-adenosyl-L-methionine + (RS)-1-benzyl-1,2,3,4-tetrahydroisoquinoline = S-adenosyl-L-homocysteine + N-methyl-(RS)-1-benzyl-1,2,3,4-tetrahydroisoquinoline
Other name(s): norreticuline N-methyltransferase
Systematic name: S-adenosyl-L-methionine:(RS)-1-benzyl-1,2,3,4-tetrahydroisoquinoline N-methyltransferase
Comments: Broad substrate specificity for (RS)-1-benzyl-1,2,3,4-tetrahydroisoquinolines; including coclaurine, norcoclaurine, isococlaurine, norarmepavine, norreticuline and tetrahydropapaverine. Both R- and S-enantiomers are methylated. The enzyme participates in the pathway leading to benzylisoquinoline alkaloid synthesis in plants. The physiological substrate is likely to be coclaurine. The enzyme was earlier termed norreticuline N-methyltransferase. However, norreticuline has not been found to occur in nature and that name does not reflect the broad specificity of the enzyme for (RS)-1-benzyl-1,2,3,4-tetrahydroisoquinolines.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 132084-82-3
References:
1.  Frenzel, T., Zenk, M.H. Purification and characterization of three isoforms of S-adenosyl-L-methionine: (R,S)-tetrahydrobenzyl-isoquinoline N-methyltransferase from Berberis koetineana cell cultures. Phytochemistry 29 (1990) 3491–3497.
[EC 2.1.1.115 created 1999]
 
 
EC 2.1.1.128     
Accepted name: (RS)-norcoclaurine 6-O-methyltransferase
Reaction: S-adenosyl-L-methionine + (RS)-norcoclaurine = S-adenosyl-L-homocysteine + (RS)-coclaurine
For diagram of reticuline biosynthesis, click here
Glossary: norcoclaurine = 6,7-dihydroxy-1-[(4-hydroxyphenyl)methyl]-1,2,3,4-tetrahydroisoquinoline
Systematic name: S-adenosyl-L-methionine:(RS)-norcoclaurine 6-O-methyltransferase
Comments: The enzyme will also catalyse the 6-O-methylation of (RS)-norlaudanosoline to form 6-O-methyl-norlaudanosoline, but this alkaloid has not been found to occur in plants.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 89700-33-4
References:
1.  Rueffer, M., Nagakura, N., Zenk, M.H. Partial purification and properties of S-adenosyl-L-methionine:(R),(S)-norlaudanosoline-6-O-methyltransferase from Argemone platyceras cell cultures. Planta Med. 49 (1983) 131–137. [PMID: 17405035]
2.  Sato, F., Tsujita, T., Katagiri, Y., Yoshida, S. and Yamada, Y. Purification and characterization of S-adenosyl-L-methionine:norcoclaurine 6-O-methyltransferase from cultured Coptis japonica cells. Eur. J. Biochem. 225 (1994) 125–131. [DOI] [PMID: 7925429]
3.  Stadler, R., Zenk, M.H. A revision of the generally accepted pathway for the biosynthesis of the benzyltetrahydroisoquinoline reticuline. Liebigs Ann. Chem. (1990) 555–562.
[EC 2.1.1.128 created 1999]
 
 
EC 2.1.1.140     
Accepted name: (S)-coclaurine-N-methyltransferase
Reaction: S-adenosyl-L-methionine + (S)-coclaurine = S-adenosyl-L-homocysteine + (S)-N-methylcoclaurine
For diagram of reticuline-biosynthesis pathway, click here
Systematic name: S-adenosyl-L-methionine:(S)-coclaurine-N-methyltransferase
Comments: The enzyme is specific for the (S)-isomer of coclaurine. Norcoclaurine can also act as an acceptor.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 167398-06-3
References:
1.  Loeffler, S., Deus-Neumann, B. and Zenk, M.H. S-Adenosyl-L-methionine: (S)-coclaurine-N-methyltransferase from Tinospora cordifolia. Phytochemistry 38 (1995) 1387–1395.
[EC 2.1.1.140 created 2001]
 
 
EC 2.1.1.291     
Accepted name: (R,S)-reticuline 7-O-methyltransferase
Reaction: (1) S-adenosyl-L-methionine + (S)-reticuline = S-adenosyl-L-homocysteine + (S)-laudanine
(2) S-adenosyl-L-methionine + (R)-reticuline = S-adenosyl-L-homocysteine + (R)-laudanine
For diagram of laudanine biosynthesis, click here
Glossary: (S)-reticuline = (1S)-1-[(3-hydroxy-4-methoxyphenyl)methyl]-6-methoxy-2-methyl-1,2,3,4-tetrahydroisoquinolin-7-ol
(R)-reticuline = (1R)-1-[(3-hydroxy-4-methoxyphenyl)methyl]-6-methoxy-2-methyl-1,2,3,4-tetrahydroisoquinolin-7-ol
(S)-laudanine = 5-[((1S)-6,7-dimethoxy-2-methyl-1,2,3,4-tetrahydroisoquinolin-1-yl)methyl]-2-methoxyphenol
(R)-laudanine = 5-[((1R)-6,7-dimethoxy-2-methyl-1,2,3,4-tetrahydroisoquinolin-1-yl)methyl]-2-methoxyphenol
Systematic name: S-adenosyl-L-methionine:(R,S)-reticuline 7-O-methyltransferase
Comments: The enzyme from the plant Papaver somniferum (opium poppy) methylates (S)- and (R)-reticuline with equal efficiency and is involved in the biosynthesis of tetrahydrobenzylisoquinoline alkaloids.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Ounaroon, A., Decker, G., Schmidt, J., Lottspeich, F. and Kutchan, T.M. (R,S)-Reticuline 7-O-methyltransferase and (R,S)-norcoclaurine 6-O-methyltransferase of Papaver somniferum - cDNA cloning and characterization of methyl transfer enzymes of alkaloid biosynthesis in opium poppy. Plant J. 36 (2003) 808–819. [DOI] [PMID: 14675446]
2.  Weid, M., Ziegler, J. and Kutchan, T.M. The roles of latex and the vascular bundle in morphine biosynthesis in the opium poppy, Papaver somniferum. Proc. Natl. Acad. Sci. USA 101 (2004) 13957–13962. [DOI] [PMID: 15353584]
[EC 2.1.1.291 created 2013]
 
 
EC 4.2.1.78     
Accepted name: (S)-norcoclaurine synthase
Reaction: 4-hydroxyphenylacetaldehyde + dopamine = (S)-norcoclaurine + H2O
For diagram of reaction, click here
Glossary: dopamine = 4-(2-aminoethyl)benzene-1,2-diol
Other name(s): (S)-norlaudanosoline synthase; 4-hydroxyphenylacetaldehyde hydro-lyase (adding dopamine)
Systematic name: 4-hydroxyphenylacetaldehyde hydro-lyase [adding dopamine; (S)-norcoclaurine-forming]
Comments: The reaction makes a six-membered ring by forming a bond between C-6 of the 3,4-dihydroxyphenyl group of the dopamine and C-1 of the aldehyde in the imine formed between the substrates. The product is the precursor of the benzylisoquinoline alkaloids in plants. The enzyme, formerly known as (S)-norlaudanosoline synthase, will also catalyse the reaction of 4-(2-aminoethyl)benzene-1,2-diol + (3,4-dihydroxyphenyl)acetaldehyde to form (S)-norlaudanosoline, but this alkaloid has not been found to occur in plants.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 79122-01-3
References:
1.  Stadler, R., Zenk, M.H. A revision of the generally accepted pathway for the biosynthesis of the benzyltetrahydroisoquinoline reticuline. Liebigs Ann. Chem. (1990) 555–562.
2.  Stadler, R., Kutchan, T.M., Zenk, M.H. (S)-Norcoclaurine is the central intermediate in benzylisoquinoline alkaloid biosynthesis. Phytochemistry 28 (1989) 1083–1086.
3.  Samanani, N. and Facchini, P.J. Purification and characterization of norcoclaurine synthase. The first committed enzyme in benzylisoquinoline alkaloid biosynthesis in plants. J. Biol. Chem. 277 (2002) 33878–33883. [DOI] [PMID: 12107162]
[EC 4.2.1.78 created 1984, modified 1999]
 
 


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