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Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
Metabolic Modeling Tutorial
discounted EARLY registration ends Dec 31, 2014
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MetaCyc Enzyme: cytokinin trans-hydroxylase

Gene: CYP735A1 Accession Number: AT5G38450 (MetaCyc)

Species: Arabidopsis thaliana col

Summary:
The major natural cytokinins are adenine derivatives that carry an isoprene-derived side chain at the N6 terminus. Small side chain variations exist including the absence or presence of a hydroxyl group at the end of the prenyl side chain and the stereoisomeric position of this hydroxyl group. This hydroxylation step is achieve by cytokinin hydroxylases. trans-zeatin is thought to play a central physiological role as well as one of the major cytokinins. trans-Zeatin is trans-hydroxylated. The protein encoded by the Arabidopsis CYP735A1 gene has been shown to act as a cytokinin trans-hydroxylase able to catalyze the stereospecific conversion of isopentenyladenosine-5'-mono-, di- or triphosphate (iPMP, iPDP or iPTP) into their respective trans-hydroxylated products: trans-zeatin-riboside mono-, di- or triphosphate [Takei04]. iPMP and iPDP were processed more efficiently than iPTP. Additionally, this enzyme was also shown to perform the hydroxylation of the dephosphorylated form those substrates albeit with drastically reduced efficiency [Takei04]. The presence of NADPH was shown to be essential for activity of this protein. In its absence NADH could only partially restore activity. The activity of this enzyme was determined from microsomal fractions prepared from Arabidopsis roots [Takei04].

Unification Links: TAIR:at5g38450

Gene-Reaction Schematic: ?


Enzymatic reaction of: isopentenyladenosine-5'-triphosphate-hydroxylase (cytokinin trans-hydroxylase)

N6-(Δ2-isopentenyl)-adenosine 5'-triphosphate + NADPH + H2O <=> trans-zeatin riboside triphosphate + NADP+ + 3 H+

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 favored in the direction shown.

In Pathways: trans-zeatin biosynthesis

Summary:
Isopentenyladenosine triphosphate (iPTP) was not processed as efficiently as its monophosphate and diphosphate counterparts [Takei04].

Kinetic Parameters:

Substrate
Km (μM)
N6-(Δ2-isopentenyl)-adenosine 5'-triphosphate
8.32


Enzymatic reaction of: N6-(dimethylallyl)adenosine 5'-phosphate-hydroxylase (cytokinin trans-hydroxylase)

Synonyms: e

N6-(Δ2-isopentenyl)-adenosine 5'-monophosphate + NADPH + H2O <=> trans-zeatin riboside monophosphate + NADP+ + 3 H+

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 favored in the direction shown.

In Pathways: trans-zeatin biosynthesis

Summary:
Metyrapone, an inhibitor of cytochrome P450 monooxygenase, was shown to inhibit this reaction. It would also appear that CYP735A1 is more sensitive to this inhibitor than CYP735A2.

Inhibitors (Unknown Mechanism): metyrapone [Takei04]

Kinetic Parameters:

Substrate
Km (μM)
Citations
N6-(Δ2-isopentenyl)-adenosine 5'-monophosphate
1.76
[Takei04]


Enzymatic reaction of: isopentenyladenosine-5'-diphosphate-hydroxylase (cytokinin trans-hydroxylase)

N6-(Δ2-isopentenyl)-adenosine 5'-diphosphate + NADPH + H2O <=> trans-zeatin riboside diphosphate + NADP+ + 3 H+

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 favored in the direction shown.

In Pathways: trans-zeatin biosynthesis

Kinetic Parameters:

Substrate
Km (μM)
Citations
N6-(Δ2-isopentenyl)-adenosine 5'-diphosphate
2.28
[Takei04]


References

Takei04: Takei K, Yamaya T, Sakakibara H (2004). "Arabidopsis CYP735A1 and CYP735A2 encode cytokinin hydroxylases that catalyze the biosynthesis of trans-Zeatin." J Biol Chem 279(40);41866-72. PMID: 15280363


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, biocyc13.