\frac{dx_{1}}{dt} = \left(1 \cdot k_{2} + -1 \cdot k_{3} \cdot x_{1} + 1 \cdot x_{1} / \left(k_{4} + x_{1}\right) + -1 \cdot k_{5} \cdot x_{1} / \left(k_{6} + k_{7} \cdot x_{1}\right)\right) / k_{1}