The model contains one compartment called C. There are four species called S1, S2, S3 and S4 and four parameters called k1, k2, kf and kr. The model contains two reactions defined as:

Reaction Rate
S1 ↔ S2 (kf · S1 − kr · S2) · C
S3 ↔ S4 (k1 · S3 − k2 · S4) · C

The model contains one event that assigns values to both species S2 and S4:

Trigger Delay Assignments
Event1 S1 < 0.5 S2 = 1.5
S4 = S2

Note that the event assignments should happen simultaneously, not sequentially; i.e., the value of S2 assigned to S4 is the value at the point at which the event was triggered.

The initial conditions are as follows:

Value Units
Initial amount of S1 1.0 mole
Initial amount of S2 2.0 mole
Initial amount of S3 1.0 mole
Initial amount of S4 1.5 mole
Value of parameter k1 0.75 second-1
Value of parameter k2 0.15 second-1
Value of parameter kf 0.9 second-1
Value of parameter kr 0.075 second-1
Volume of compartment C 1 litre

The species values are given as amounts of substance to make it easier to use the model in a discrete stochastic simulator, but (as per usual SBML principles) their symbols represent their values in concentration units where they appear in expressions.