\frac{dx_{1}}{dt} = \left(-1 \cdot k_{7} \cdot k_{8} \cdot x_{1} + 1 \cdot k_{7} \cdot k_{1} \cdot x_{3} + 1 \cdot k_{7} \cdot k_{6} \cdot x_{4}\right) / k_{7}\\
\frac{dx_{2}}{dt} = \left(-1 \cdot k_{7} \cdot k_{9} \cdot x_{2} + 1 \cdot k_{7} \cdot k_{2} \cdot x_{4}\right) / k_{7}\\
\frac{dx_{3}}{dt} = \left(-1 \cdot k_{7} \cdot k_{10} \cdot x_{3} + 1 \cdot k_{7} \cdot k_{12} / \left(k_{13}^{k_{4}} + x_{2}^{k_{4}}\right)\right) / k_{7}\\
\frac{dx_{4}}{dt} = \left(-1 \cdot k_{7} \cdot k_{11} \cdot x_{4} + 1 \cdot k_{7} \cdot k_{15} \cdot x_{1}^{k_{5}} / \left(k_{14}^{k_{5}} + x_{1}^{k_{5}}\right)\right) / k_{7}