\frac{dx_{1}}{dt} = \left(1 \cdot k_{5} \cdot k_{1} \cdot x_{2} + 1 \cdot k_{5} \cdot k_{2} \cdot x_{2} \cdot x_{1}^{2} + -1 \cdot k_{5} \cdot k_{3} \cdot x_{1} / \left(x_{1} + 1\right)\right) / k_{5}\\
\frac{dx_{2}}{dt} = \left(1 \cdot k_{5} \cdot k_{4} + -1 \cdot k_{5} \cdot x_{1}\right) / k_{5}