MMR

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What we know

Menthone: menthol reductase(s) (MMR) catalyses the NADPH-dependent convertion of menthone to menthol and the conversion of isomenthone to isomenthol.

Reaction catalysed

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

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

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
menthone:menthol reductase	MMR		34070 Da , 35000 Da				1.1.1.207
menthone
isomenthone
NADPH		C21H30N7O17P3	745.42116	16474
NADP+		C21H29N7O17P3	744.41322	18009

Equation Rate

Two MMR reactions are included in the kinetic model with one converting menthone to menthol and isomenthone, and one converting isomenthone to isomenthol. Both reactions are parameterised using random Bi-Bi reversible Michaelis-Menten equation.

Reaction 1: Conversion of menthone to menthol

Failed to parse (Cannot store math image on filesystem.): V_\mathrm{MMR} = Kcat_\mathrm{forward} * [MMR] * \cfrac {\left ( \cfrac{[menthone]}{Km_\mathrm{menthone}} * \cfrac {[NADPH]}{Km_\mathrm{NADPH}} \right ) * \left ( 1 - \cfrac {[menthol]*[NADP]}{[menthone]*[NADPH]*K_\mathrm{eq}} \right )} { \left (1 + \cfrac {[NADPH]}{Km_\mathrm{NADPH}} + \cfrac {[NADP]}{Km_\mathrm{NADP}} \right ) + \left ( 1+ \cfrac {[menthone]}{Km_\mathrm{menthol}} + \cfrac {[menthol]}{Km_\mathrm{menthol}} \right ) }

Reaction 2: Conversion of isomenthone to isomenthol

$V_\mathrm{MMR} = Kcat_\mathrm{forward} * [MMR] * \cfrac {\left ( \cfrac{[isomenthone]}{Km_\mathrm{isomenthone}} * \cfrac {[NADPH]}{Km_\mathrm{NADPH}} \right ) * \left ( 1 - \cfrac {[isomenthol]*[NADP]}{[isomenthone]*[NADPH]*K_\mathrm{eq}} \right )} { \left (1 + \cfrac {[NADPH]}{Km_\mathrm{NADPH}} + \cfrac {[NADP]}{Km_\mathrm{NADP}} \right ) + \left ( 1+ \cfrac {[isomenthone]}{Km_\mathrm{isomenthone}} + \cfrac {[isomenthol]}{Km_\mathrm{isomenthol}} \right ) }$

Parameter	Description	Units
VMMR	Reaction rate for MMR	μM/min
Kcatforward	Catalytic constant in the forward direction	s-1
Kmmenthone	Michaelis-Menten constant for menthone	μM
Kmmenthol	Michaelis-Menten constant for menthol	μM
Kmisomenthone	Michaelis-Menten constant for isomenthone	μM
Kmisomenthol	Michaelis-Menten constant for isomenthol	μM
KmNADPH	Michaelis-Menten constant for NADPH	μM
KmNADP	Michaelis-Menten constant for NADP+	μM
Keq	Equilibrium constant
[MMR]	enzyme concentration	μM
[menthol]	menthol concentration	μM
[menthone]	Menthone concentration	μM
[isomenthone]	Isomenthone concentration	μM
[isomenthol]	Isomenthol concentration	μM
[NADPH]	NADPH concentration	μM
[NADP]	NADP+ concentration	μM

Strategies for estimating the kinetic parameter values

Estimating parameters for MMR

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 menthone Production Rates

A table will go here

Published Kinetic Parameter Values

Km Values

Parameter	Directionality	Substrate / Product	Value	unit	Method notes	References

Detailed description of kinetic values obtained from literature

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