Now, what we see happen is the NH groups that are basically found on the backbone of this pilot will interact, will form hydrogen bonds with the negative charges of these oxygen on the triphosphate. And likewise, if we have any residue that contains a positive charge. So if we have basic residues such as lysine and arginine found on a PLOOP, those will also form interactions with this triphosphate. And so it's the p loop structure found inside this domain of the enzyme that actually is responsible for binding and interacting with this substrate molecule, the triphosphate group of that particular nucleotide triphosphate. So in the case of adenylate kinase, it's the triphosphate group of the ATP that the p loop actually interacts with. Now, the second thing you have to know about nucleoside monophosphate kinases is they use a specific mechanism of enzyme catalysis known as metal ion catalysis.