Double-bond reductase (DBR)

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What we know

Pulegone reductase(s) (PGR) catalyses the NADPH-dependent convertion of pulegone to menthone and isomenthone (the former predominates).

Reaction catalysed

$pulegone + NADPH \rightleftharpoons menthone + NADP^+$

$pulegone + NADPH \rightleftharpoons isomenthone + NADP^+$

Enzyme and Metabolite Background Information

Long metabolite names are abbreviated in the model for clarity and standard identification purposes.

Metabolite	Abbreviation	Chemical Formula	Molar mass (g/mol)	ChEBI	ChEMBL	PubChem	BRENDA	PlantCyc
pulegone reductase	PGR		37914 Da				1.3.1.81
pulegone		C10H16O	136.24
menthone
NADPH		C21H30N7O17P3	745.42116	16474
NADP+		C21H29N7O17P3	744.41322	18009
isomenthone

Equation Rate

Limonene-hydroxylase (L3H) is modelled using the reversible Michaelis-Menten equation.

$V_\mathrm{L3H} = Vmax_\mathrm{forward} * \cfrac {\left ( \cfrac{[limonene]}{Km_\mathrm{limonene}} * \cfrac {[NADPH]}{Km_\mathrm{NADPH}} \right ) * \left ( 1 - \cfrac {[isopiperitenol]*[NADP]}{[limonene]*[NADPH]*K_\mathrm{eq}} \right )} { \left (1 + \cfrac {[NADPH]}{Km_\mathrm{NADPH}} + \cfrac {[NADP]}{Km_\mathrm{NADP}} \right ) + \left ( 1+ \cfrac {[limonene]}{Km_\mathrm{limonene}} + \cfrac {[isopiperitenol]}{Km_\mathrm{isopiperitenol}} \right ) }$

Parameter	Description	Reference
VL3H	Reaction rate for Limonene-3-hydroxylase	ref
Vmaxforward	Maximum reaction rate towards the production of (-)-trans-isopiperitenol	ref
Kmlimonene	Michaelis-Menten constant for Limonene	ref
Kmisopiperitenol	Michaelis-Menten constant for (-)-trans-isopiperitenol	ref
KmNADPH	Michaelis-Menten constant for NADPH	ref
KmNADP	Michaelis-Menten constant for NADP+	ref
Keq	Equilibrium constant	ref
[limonene]	Limonene concentration	ref
[isopiperitenol]	(-)-trans-isopiperitenol concentration	ref
[NADPH]	NADPH concentration	ref
[NADP]	NADP+ concentration	ref

Strategies for estimating the kinetic parameter values

Standard Gibbs Free energy

The Gibbs free energy for PGR is -3.9565125 kcal.mol^-1. This value is estimated from the 'Contribution group' method by Latendresse, M. and is available from MetaCyc (EC 1.3.1.81) .

Calculating the Equilibrium Constant

The equilibrium constant can be calculated using the Van't Hoff Isotherm equation:

$K_\mathrm{eq} = exp \left ( \cfrac {-ΔG^{°'}}{RT} \right )$

$= exp \left ( \cfrac {-(XY \text { kJmol}^{-1})}{ (8.31 \text{ JK}^{-1} \text { mol}^{-1} * 289 K} \right )$

$= exp \left ( \cfrac { XY \text { kJmol}^{-1} }{ 2401.59 \text{ JK}^{-1}\text { mol}^{-1} }\right)$

$= exp \left ( \cfrac{ XY \text { Jmol}^{-1}}{2401.59 \text{ JK}^{-1}\text { mol}^{-1}} \right)$

$=exp \left ( XY \right )$

$= (INSERT RESULT)$

where;

Keq	Equilibrium constant
-ΔG°	Gibbs free energy change. For (INSERT ENZYME) it is (INSERT VALUE) kJmol-1
R	Gas constant with a value of 8.31 JK-1mol-1
T	Temperature which is always expressed in kelvin

Extracting Information from (INSERT SUBSTRATE/PRODUCT) Production Rates

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Published Kinetic Parameter Values

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Detailed description of kinetic values obtained from literature

A more detailed description of the values listed above can be found here .