\frac{dx_{1}}{dt} = \left(1 \cdot k_{26} \cdot k_{5} \cdot x_{1} \cdot \left(1 - x_{1} / k_{6}\right) + -1 \cdot k_{26} \cdot k_{1} \cdot k_{3} \cdot x_{1} / \left(k_{4} + k_{2} \cdot x_{1}\right) + -1 \cdot k_{26} \cdot k_{7} \cdot x_{2} / \left(1 + x_{4} / k_{17}^{2}\right) \cdot x_{1}\right) / k_{26}\\
\frac{dx_{2}}{dt} = \left(1 \cdot k_{26} \cdot k_{10} \cdot \left(k_{9} \cdot x_{2} + k_{8} \cdot x_{1} + k_{13} \cdot x_{3}\right) / \left(1 + x_{4} / k_{17}^{2}\right) / \left(k_{11} + \left(k_{9} \cdot x_{2} + k_{8} \cdot x_{1} + k_{13} \cdot x_{3}\right) / \left(1 + x_{4} / k_{17}^{2}\right)\right) + -1 \cdot k_{26} \cdot k_{12} \cdot x_{2}\right) / k_{26}\\
\frac{dx_{3}}{dt} = \left(1 \cdot k_{26} \cdot k_{14} \cdot x_{2} / \left(1 + x_{4} / k_{17}^{2}\right)^{6} / \left(k_{15}^{6} + x_{2} / \left(1 + x_{4} / k_{17}^{2}\right)^{6}\right) + -1 \cdot k_{26} \cdot k_{16} \cdot x_{3}\right) / k_{26}\\
\frac{dx_{4}}{dt} = \left(1 \cdot k_{26} \cdot k_{18} + 1 \cdot k_{26} \cdot k_{19} \cdot \left(x_{2} + k_{20} \cdot x_{3}\right) / \left(1 + x_{4} / k_{17}^{2}\right) / \left(1 + \left(x_{2} + k_{20} \cdot x_{3}\right) / \left(1 + x_{4} / k_{17}^{2}\right)\right) + -1 \cdot k_{26} \cdot k_{21} \cdot x_{4}\right) / k_{26}