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