\frac{dx_{1}}{dt} = \left(1 \cdot k_{8} \cdot k_{1} \cdot x_{1}^{4 / 5} + -1 \cdot k_{8} \cdot k_{2} \cdot x_{2} \cdot x_{1} / \left(1 + x_{2} / k_{3} + x_{1} / k_{3}\right)\right) / k_{8}\\
\frac{dx_{2}}{dt} = \left(1 \cdot k_{7} \cdot x_{3} + -1 \cdot k_{8} \cdot k_{4} \cdot x_{2}\right) / k_{8}\\
\frac{dx_{3}}{dt} = \left(-1 \cdot k_{7} \cdot x_{3} + 1 \cdot k_{5} \cdot x_{1} / \left(10000000 + x_{1}\right) \cdot x_{4} + 1 \cdot k_{9} \cdot k_{6} \cdot x_{3}\right) / k_{9}\\
\frac{dx_{4}}{dt} = -1 \cdot k_{5} \cdot x_{1} / \left(10000000 + x_{1}\right) \cdot x_{4} / k_{9}