    \begin{equation} \label{repression}
      \begin{array}{l}\displaystyle 
            \text{G} \mathop{\longrightarrow}^{k_{1}} \text{G} + \text{P} \\ \displaystyle 
          	\text{R} + \text{G} \mathop{\rightleftarrows}^{k_{2}}_{k_{-2}} \text{G}_{\text{R}} \\ \displaystyle
            \text{P} \mathop{\longrightarrow}^{d}%\xrightarrow{\text{k}_3} 
         \end{array}
    \end{equation}
