And that means they bind very, very, very tightly, very, very strongly. And even if we remove access inhibitor from that mixture, that will not dissociate that inhibitor, that will not reform that active version of the enzyme. So, all the different types of inhibitors, irreversible inhibitors that we have in nature and that we can synthesize in a lab, can basically be categorized into three different groups, into three different categories. We have group specific inhibitors. We have substrate analogs, also known as affinity labels, and we have suicide inhibitors, also known as mechanism based inhibitors. Now, we can actually use these three different types of Irreversible inhibitors to actually probe and study the residues found inside active sites of enzymes.