\frac{dx_{1}}{dt} = \left(1 \cdot \left(k_{10} \cdot x_{3} + k_{1} \cdot x_{1} \cdot x_{2} / \left(k_{2} + x_{2}\right)\right) + -1 \cdot k_{13} \cdot \left(k_{3} \cdot x_{1} \cdot x_{2} / \left(k_{4} + x_{1}\right) + 1 / k_{5} \cdot x_{1}\right)\right) / k_{13}\\
\frac{dx_{2}}{dt} = \left(1 \cdot k_{13} \cdot k_{6} \cdot x_{2} + -1 \cdot k_{13} \cdot k_{7} \cdot x_{1} \cdot x_{2}\right) / k_{13}\\
\frac{dx_{3}}{dt} = \left(1 \cdot k_{14} \cdot k_{8} \cdot x_{3} \cdot x_{4} / \left(k_{9} + x_{4}\right) + -1 \cdot k_{14} \cdot \left(1 / k_{5} \cdot x_{3} + k_{10} \cdot x_{3}\right)\right) / k_{14}\\
\frac{dx_{4}}{dt} = -1 \cdot k_{14} \cdot \left(k_{11} \cdot x_{4} \cdot x_{3} + 1 / k_{12} \cdot x_{4}\right) / k_{14}