A kinetic model of the branch-point between the methionine and threonine biosynthesis pathways in Arabidopsis thaliana

Model Status

This model contains no ODEs, and as such can not currently be solved by any of the available CellML tools.

ValidateCellMl verifies this model as valid CellML with full unit consistency.

Model Structure

Metabolic branch-points are highly diverse in terms of the enzymes involved, the kinetic mechanisms of the competing enzymes, and the nature of the allosteric controls. How such diversity in organisation affects variation in branch-point kinetics is not well understood. In the Curien et al. 2003 publication described here, the authors present a kinetic model of the branch-point between the methionine and threonine biosynthesis pathway in Arabidopsis thaliana (see the figure below).

The pathway branch-point involves two enzymes: cystathionine gamma-synthase (CGS), and threonine synthase (TS). These two enzymes compete for the substrate phosphohomoserine (Phser), in chloroplasts. CGS catalyses the formation of cystathionine, the precursor of methionine (Met) and S-adenosylmethionine (AdoMet). In the competing branch, TS catalyses the synthesis of threonine. TS is stimulated by AdoMet, and both TS and CGS are inhibited by inorganic phosphate (Pi). In addition, TS is inhibited by AMP, which competes with AdoMet for its binding site on the enzyme.

The model has been described here in CellML and showed partial agreement when simulation results were compared with in vitro experimental results.

The complete original paper reference is cited below:

A Kinetic Model of the Branch-Point between the Methionine and Threonine Biosynthesis Pathways in Arabidopsis thaliana , Gilles Curien, Stephane Ravanel and Renaud Dumas, 2003, European Journal of Biochemistry , 270, 4615-4627. PubMed ID: 14622248

Schematic diagram of the Phser branch-point in the aspartate-derived amino acid biosynthetic pathway in plants.