Model number


Contains four xanthine oxidase models: MM2Substrate_irreversible (Model #0320), MM2substrate_product_inhibited (Model #0321), Vfnet_MM2substrate_reversible (Model #0322), FullXO (Model #0323)


The four models contained here describe in increasing detail the reactions facilitated by Xanthine Oxidase. The fourth model, FullXO (model #323) is the only thermodynamically correct one. All four models give similar estimates of fluxes but only the FullXO model accounts for binding of substrate to exzyme (The enzyme concnetration is an additional item of data and constrains the solutions).

The four models are:

  • MM2Substrate_irrevers: Single enzyme irreversible Michaelis-Menten Eqs for Hx->Xa->Ua Progress curves for xanthine oxidase reactions to oxidize hypoxanthine, Hx,to xanthine, Xa, to uric acid, Ua
  • MM2Substrate_product_Inhibited: Single enzyme irreversible Michaelis-Menten Eqs for Hx->Xa->Ua: Progress curves for xanthine oxidase reactions to oxidize hypoxanthine, Hx, to xanthine, Xa, to uric acid, Ua, and invokes inhibition by second product.(Data and equations from Escribano 1988).
  • Vfnet_MM2substrate_reversible: Single enzyme reversible Michaelis-Menten Eqs for Hx->Xa->Ua, that is, two reactions on one enzyme. Data are progress curves for xanthine oxidase reactions to oxidize hypoxanthine, Hx, to xanthine, Xa, to uric acid, Ua, without inhibition by product.(Data from Escribano 1988).
  • FullXO: Four sequential, first-order enzymatic reactions S <--> P with substrates binding to enzymes, and reversible product formation. Reactions facilitated by a single enzyme, Xanthine Oxidase.


The equations for this model may be viewed by running the JSim model applet and clicking on the Source tab at the bottom left of JSim's Run Time graphical user interface. The equations are written in JSim's Mathematical Modeling Language (MML). See the Introduction to MML and the MML Reference Manual. Additional documentation for MML can be found by using the search option at the Physiome home page.

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 Bassingthwaighte James B., Chinn Tamara Meiko, 
 Re-examining Michaelis-Menten enzyme kinetics for xanthine oxidase, 
 Adv Physiol Educ 37: 37-48, 2013

 Escribano, J., Garcia-Canovas, F., and Garcia-Carmona,F.
 A kinetic study of hypoxanthine oxidation by milk xanthine oxidase.
 Biochem. J. 254:  829-833. (1988).

 Michaelis L and Menten ML. Die Kinetik der Invertinwirkung.
 Biochem Z 49: 333-369, 1913.
Key terms
purine nucleosides
xanthine oxidase
simple Michaelis-Menten equations
double reaction
serial reactions
progress curves
bovine milk
uric acid
saturable binding

Please cite in any publication for which this software is used and send one reprint to the address given below:
The National Simulation Resource, Director J. B. Bassingthwaighte, Department of Bioengineering, University of Washington, Seattle WA 98195-5061.

Model development and archiving support at provided by the following grants: NIH U01HL122199 Analyzing the Cardiac Power Grid, 09/15/2015 - 05/31/2020, NIH/NIBIB BE08407 Software Integration, JSim and SBW 6/1/09-5/31/13; NIH/NHLBI T15 HL88516-01 Modeling for Heart, Lung and Blood: From Cell to Organ, 4/1/07-3/31/11; NSF BES-0506477 Adaptive Multi-Scale Model Simulation, 8/15/05-7/31/08; NIH/NHLBI R01 HL073598 Core 3: 3D Imaging and Computer Modeling of the Respiratory Tract, 9/1/04-8/31/09; as well as prior support from NIH/NCRR P41 RR01243 Simulation Resource in Circulatory Mass Transport and Exchange, 12/1/1980-11/30/01 and NIH/NIBIB R01 EB001973 JSim: A Simulation Analysis Platform, 3/1/02-2/28/07.