\frac{dx_{1}}{dt} = \left(1 \cdot k_{40} \cdot k_{31} \cdot x_{1} \cdot \left(1 - x_{1} / k_{32}\right) + -1 \cdot k_{40} \cdot k_{36} \cdot k_{34} \cdot x_{1} / \left(k_{35} + k_{33} \cdot x_{1}\right) + -1 \cdot k_{40} \cdot k_{1} \cdot x_{1} \cdot x_{4} \cdot \left(1 + k_{25} \cdot k_{38}\right) + -1 \cdot k_{40} \cdot k_{2} \cdot x_{1} \cdot x_{3} / \left(1 + x_{4} / k_{3}^{2} + k_{37} / k_{29}^{2}\right) \cdot \left(1 + k_{27} \cdot k_{38}\right)\right) / k_{40}\\
\frac{dx_{2}}{dt} = \left(-1 \cdot k_{40} \cdot k_{4} \cdot x_{2} \cdot x_{4} \cdot \left(1 + k_{25} \cdot x_{4}\right) + -1 \cdot k_{40} \cdot k_{5} \cdot x_{2} \cdot x_{3} / \left(1 + x_{4} / k_{3}^{2} + k_{37} / k_{29}^{2}\right) \cdot \left(1 + k_{27} \cdot k_{38}\right) + 1 \cdot k_{40} \cdot k_{11} \cdot x_{4} + -1 \cdot k_{40} \cdot k_{6} \cdot x_{2}\right) / k_{40}\\
\frac{dx_{3}}{dt} = \left(1 \cdot k_{40} \cdot k_{17} \cdot \left(k_{16} \cdot x_{2} + k_{13} \cdot x_{1} + k_{14} / \left(1 + k_{38} / k_{26}^{2}\right) \cdot x_{3} + k_{15} \cdot x_{4}\right) / \left(1 + k_{37} / k_{30}^{2}\right) / \left(k_{18} + \left(k_{16} \cdot x_{2} + k_{13} \cdot x_{1} + k_{14} / \left(1 + k_{38} / k_{26}^{2}\right) \cdot x_{3} + k_{15} \cdot x_{4}\right) / \left(1 + k_{37} / k_{30}^{2}\right)\right) + -1 \cdot k_{40} \cdot k_{19} \cdot x_{3}\right) / k_{40}\\
\frac{dx_{4}}{dt} = \left(-1 \cdot k_{40} \cdot k_{11} \cdot x_{4} + 1 \cdot k_{40} \cdot k_{9} \cdot \left(k_{8} \cdot x_{2} + k_{7} \cdot x_{1}\right) / \left(1 + k_{37} / k_{28}^{2}\right) / \left(k_{10} + \left(k_{8} \cdot x_{2} + k_{7} \cdot x_{1}\right) / \left(1 + k_{37} / k_{28}^{2}\right)\right) / \left(1 + k_{38} / k_{24}^{2}\right) + -1 \cdot k_{40} \cdot k_{12} \cdot x_{4} \cdot x_{3} / \left(1 + x_{4} / k_{3}^{2} + k_{37} / k_{29}^{2}\right)\right) / k_{40}