So how does that actually take place? Well, in a similar way to how it takes place in seren proteases, so we have a nearby residue, for example, a histidine. And on that histidine, we have this nitrogen, which contains a lone pair of electrons. On top of that, the nitrogen can also have or also has a partial negative charge because it's more electronegative than the nearby carbon atoms. Now, if we examine this H on the sulfur, we see that the age contains a partial positive charge because the sulfur is more electronegative and the sulfur contains a partial negative charge. So what we see happening is before the substrate actually enters the active side, what begins to happen is the nitrogen, because of its higher electron density, begins to pull on this H ion.