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MetaCyc Enzyme: gibberellin carboxyl methyltransferase

Gene: GAMT2 Accession Number: AT5G56300

Species: Arabidopsis thaliana col

Summary:
The GAMT2 enzyme, a member of the SABATH family of carboxyl methyltransferases, is involved in methylating several gibberellins (GAs) that belong to an important class of plant hormones [Varbanova07]. In vitro experiments demonstrate that this enzyme can add a methyl group to the free carboxyl group at position 7 on gibberellins that are hydroxylated at position C13 (such as gibberellin A1) and those that are not (such as gibberellin A4). It has its lowest Km with gibberellin A9, but it also appears to work well with gibberellin A4 and has a lower Kcat / Km with this substrate [Varbanova07] It also had a high level of activity with gibberellin A34 .

GAMT2 transcript expression is largely limited to the later stages of silique development in Arabidopsis plants, indicating that this enzyme may be active during seed development [Varbanova07].

Mutant analyses confirm an in vivo role for GAMT2 in gibberellin metabolism. Plants over-expressing GAMT2 have reduced levels of the bioactive gibberellin A4, and they are dwarfed and largely sterile, consistent with reduced levels of endogenous GAs. In addition, a double mutant that lacks GAMT2 and its close homolog GAMT1 has elevated levels of bioactive gibberellin A4 and gibberellin A1 in its siliques [Varbanova07]. Althought the GAMT1 and GAMT2 proteins are quite similar (59% amino acid identity), it is possible that they play specialized roles in planta. For instance, Arabidopsis plants over-expressing the GAMT1 gene had a more pronounced reduction in the level of a greater number of different gibberellins than plants over-expressing GAMT2 [Varbanova07].

Molecular Weight of Polypeptide: 43.3 kD (from nucleotide sequence)

Unification Links: ArrayExpress:Q5XF78 , PhylomeDB:Q5XF78 , Pride:Q5XF78 , Protein Model Portal:Q5XF78 , SMR:Q5XF78 , String:3702.AT5G56300.1-P , TAIR:AT5G56300 , UniProt:Q5XF78

Relationship Links: InterPro:IN-FAMILY:IPR005299 , Pfam:IN-FAMILY:PF03492

Gene-Reaction Schematic: ?

Credits:
Created 14-Apr-2010 by Dreher KA , TAIR


Enzymatic reaction of: GA4 carboxyl methyltransferase (gibberellin carboxyl methyltransferase)

Synonyms: gibberellin A4 carboxyl methyltransferase

EC Number: 2.1.1.-

gibberellin A34 + S-adenosyl-L-methionine <=> methyl gibberellin A34 + S-adenosyl-L-homocysteine

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the direction in which it was curated.

The reaction is physiologically favored in the direction shown.

Alternative Substrates for gibberellin A34: gibberellin A3 [Varbanova07 ] , gibberellin A1 [Varbanova07 ] , gibberellin A51 [Varbanova07 ] , gibberellin A20 [Varbanova07 ]

In Pathways: gibberellin inactivation II (methylation)


Enzymatic reaction of: GA4 carboxyl methyltransferase (gibberellin carboxyl methyltransferase)

Synonyms: gibberellin A4 carboxyl methyltransferase

EC Number: 2.1.1.276

gibberellin A4 + S-adenosyl-L-methionine <=> methyl gibberellin A4 + S-adenosyl-L-homocysteine

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is physiologically favored in the direction shown.

In Pathways: gibberellin inactivation II (methylation)

Summary:
The enzyme had a Kcat of 1.5 x 10-3 s-1 and a Kcat / Km of 0.2 nM-1 s-1 [Varbanova07].

Activators (Unknown Mechanism): Zn2+ [Varbanova07] , Cu2+ [Varbanova07]

Inhibitors (Unknown Mechanism): Fe3+ [Varbanova07]

Kinetic Parameters:

Substrate
Km (μM)
gibberellin A4
5.9

pH(opt): 8.0 [Varbanova07]


Enzymatic reaction of: GA9 carboxyl methyltransferase (gibberellin carboxyl methyltransferase)

Synonyms: gibberellin A9 carboxyl methyltransferase

EC Number: 2.1.1.275

gibberellin A9 + S-adenosyl-L-methionine <=> methyl gibberellin A9 + S-adenosyl-L-homocysteine

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is physiologically favored in the direction shown.

In Pathways: gibberellin inactivation II (methylation)

Summary:
The enzyme had a Kcat of 1.8 x 10-3 s-1 and a Kcat / Km of 0.9 nM-1 s-1 [Varbanova07].

Kinetic Parameters:

Substrate
Km (μM)
Citations
gibberellin A9
1.9
[Varbanova07]


References

Varbanova07: Varbanova M, Yamaguchi S, Yang Y, McKelvey K, Hanada A, Borochov R, Yu F, Jikumaru Y, Ross J, Cortes D, Ma CJ, Noel JP, Mander L, Shulaev V, Kamiya Y, Rodermel S, Weiss D, Pichersky E (2007). "Methylation of gibberellins by Arabidopsis GAMT1 and GAMT2." Plant Cell 19(1);32-45. PMID: 17220201


Report Errors or Provide Feedback
Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
Page generated by SRI International Pathway Tools version 18.5 on Thu Nov 27, 2014, BIOCYC14B.