 Biochemistry laboratories often use in vitro studies to explore ATP @-@ dependent molecular processes . Enzyme inhibitors of ATP @-@ dependent enzymes such as kinases are needed to examine the binding sites and transition states involved in ATP @-@ dependent reactions . ATP analogs are also used in X @-@ ray crystallography to determine a protein structure in complex with ATP , often together with other substrates . Most useful ATP analogs cannot be hydrolyzed as ATP would be ; instead they trap the enzyme in a structure closely related to the ATP @-@ bound state . Adenosine 5 ′ - ( γ @-@ <unk> ) is an extremely common ATP analog in which one of the gamma @-@ phosphate oxygens is replaced by a sulfur atom ; this molecule is hydrolyzed at a dramatically slower rate than ATP itself and functions as an inhibitor of ATP @-@ dependent processes . In crystallographic studies , hydrolysis transition states are modeled by the bound vanadate ion . However , caution is warranted in interpreting the results of experiments using ATP analogs , since some enzymes can hydrolyze them at appreciable rates at high concentration . 
