The Adenylate Kinase transfers a phosphate group form one compound to another. This specific enzyme catalyzes a high-energy phosphoryl transfer between adenine nucleotides:
ATP+AMP->2 ADP
This reaction cleaves a high energy bond and provides energy for the cell to undergo other processes.
+
-> 2
There are six isozymes that have been identified. They are named AK1, AK2, etc. AK1 is localized in neuron processes, located in the sperm tail, and on the cytoskeleton in cardiac cells. This suggests that it can function as a high-energy beta phosphoryl transfer chain from ATP-synthesizing sites to ATP-utilizing sites within a cell. AK2,3, and 4 act as mitochondrial proteins. AK2 is found in the intermembrane space where as AK3 and AK4 are localized in the mitochondrial matrix. AK3 is expressed in all tissues except for in red blood cells. AK4 is located in tissues and is specifically located in the kidney, brain and heart. AK5 is located in the brain and AK6 has been identified in the nucleus (Journal of Medical Investigation).
Thermodynamics:
This kinetics of the AK reactions have been found to decrease with an increase in temperature. This is because, in high temperatures, the protein denatures.
Inhibitor:
The inhibitor in this enzyme is like an ATP molecule coupled to an AMP through the additional Phosphates. AP5A is a covalently symmetrical molecule and therefore it cannot distinguish between the ATP and AMP site when binding. The AP5A binds via polar contacts (Abele). The binding of AP5A results in an increase of the protection factors in the active site (Burlacu-Miron).
Structure:
There are two very important sequences that are found in each of the isoforms. The sequence GLY-GLY-PRO-ALA-PRO-GLY-SERorALA-GLY-LYS-GLY-THR-GLN is the first. These “Glycine rich” loops are found in other ATP-binding proteins are are seen to be essential for binding nucleotide substrates.
The second sequence, GLY-PHE-LEU-ILE or VAL-TYR or PHE-ASP-GLY-TYR-PRO-ARG, is found to make a Beta sheet that is essential to the large active site cleft, a Beta turn, and then an eight-residue long alpha-helix. The folding consists of a five-stranded parallel Beta-sheet with surrounding alpha-helices(Rose).