\frac{dx_{1}}{dt} = 0\\
\frac{dx_{2}}{dt} = \left(1 \cdot k_{2} \cdot k_{3} \cdot k_{8} + -1 \cdot k_{2} \cdot x_{4} \cdot k_{5} \cdot x_{2} / \left(k_{4} + x_{2}\right) + -1 \cdot k_{2} \cdot k_{7} \cdot x_{2}\right) / k_{2}\\
\frac{dx_{3}}{dt} = \left(1 \cdot k_{2} \cdot x_{4} \cdot k_{5} \cdot x_{2} / \left(k_{4} + x_{2}\right) + -1 \cdot k_{2} \cdot k_{6} \cdot x_{3}\right) / k_{2}\\
\frac{dx_{4}}{dt} = 0 / k_{2}