And that leads us to property six active sites. Active sites. This should be active sites where is my marker? So this should be active sites have structures complementary to their corresponding substrate. So in order for the non covalent interactions between the residues of the active side of the enzyme and the substrate to be meaningful and strong enough for them to actually remain attached, the distance between them must be short enough. And this implies that the substrate must fit Snugly into the active side of that particular enzyme.