As it binds onto the pilot, this basically closes down just like a lid closes on top of a can. And so, in the same way, this lid basically closes down and it induces a conformational change that traps that ATP molecule in the proper orientation so that now the other substrate, the NMP, can bind onto the active side. And it binds in such a way so that the terminal phosphoryl group of the ATP is in close proximity and in the proper orientation with respect to this and MP molecule. And that's exactly what we mean by catalysis by proximity and orientation. What the active side does is it induces this change that brings these two substrate molecules in close proximity and arranges them in a proper orientation which basically decreases the energy of transition and it basically catalyzes the transfer of this phosphoryl group from ATP onto the NMP. In addition, because these two substrate molecules are essentially trapped in the active side, nothing else can actually come in because this entire lid domain closes off.