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. And as the H ion is being pulled away onto the nitrogen, as shown in this particular diagram, these two electrons in the sigma bond move closer to the sulfur atom, and that increases the electron density, the electron cloud around the sulfur, and that increases its ability to act as a nucleophile. So as the H atom is being pulled away onto the nitrogen of the nearby histidine residue, we see that these two electrons move closer to the sulfur and the electron density on the sulfur increases. And so as we have this incoming substrate molecule these two electrons attack nucleophilically the carbon on the carbonyl and that displays the pi bond.