\frac{dx_{1}}{dt} = \left(1 \cdot k_{25} \cdot k_{15} \cdot k_{16} \cdot \left(1 - k_{17} / k_{18}\right) + -1 \cdot k_{25} \cdot k_{2} \cdot x_{1} + -1 \cdot k_{25} \cdot k_{3} \cdot x_{1} \cdot x_{3}\right) / k_{25}\\
\frac{dx_{2}}{dt} = \left(1 \cdot k_{25} \cdot \left(k_{4} + k_{5} \cdot x_{4}^{k_{6}} / \left(k_{7}^{k_{6}} + x_{4}^{k_{6}}\right)\right) + -1 \cdot k_{25} \cdot k_{8} \cdot x_{2}\right) / k_{25}\\
\frac{dx_{3}}{dt} = \left(1 \cdot k_{25} \cdot k_{9} \cdot x_{2} + -1 \cdot k_{25} \cdot k_{10} \cdot x_{3}\right) / k_{25}\\
\frac{dx_{4}}{dt} = \left(1 \cdot k_{25} \cdot k_{11} \cdot x_{5} \cdot k_{12}^{k_{13}} / \left(k_{12}^{k_{13}} + x_{1}^{k_{13}}\right) + -1 \cdot k_{25} \cdot k_{14} \cdot x_{4}\right) / k_{25}