KineticLaw

KineticLaw is a component of a Reaction in the Systems Biology Markup Language (SBML) specification. It defines the rate law that governs the reaction’s velocity, providing the mathematical expression used to compute how fast reactants are converted into products under given conditions. The KineticLaw’s value is derived from the current concentrations of participating species and the values of parameters referenced in the expression.

A KineticLaw contains a Math element, which holds a MathML-formatted expression describing the rate. This expression can represent simple forms such as mass-action kinetics, as well as more complex forms like Michaelis–Menten, Hill, or fully general user-defined formulas. The variables in the math expression typically include species identifiers and parameter identifiers defined elsewhere in the model.

Local parameters can be defined within a KineticLaw via a ListOfLocalParameters. These parameters are local to the specific law and provide rate constants or other constants needed by the expression. They are distinct from global parameters defined at the model level, though global parameters may also be referenced within the law if in scope.

In SBML, each Reaction generally has an associated KineticLaw that determines the reaction rate, with the result interpreted as a rate of change compatible with the model’s unit system. The KineticLaw is essential for encoding diverse kinetic mechanisms, enabling simulations of dynamic behavior in metabolic networks, signaling pathways, and other biological processes.