\frac{dx_{1}}{dt} = \left(1 \cdot k_{5} \cdot k_{1} + -1 \cdot k_{5} \cdot k_{2} \cdot x_{1}^{k_{4} + 1} / \left(k_{3}^{k_{4}} + x_{1}^{k_{4}}\right)\right) / k_{5}