 A number of receptor tyrosine kinases, though certainly not all, do not perform protein-kinase activity until they are occupied, or activated, by one of these ligands.Although more research indicates that receptors remain active within endosomes, it was once thought that endocytosis caused by ligands was the event responsible for the process in which receptors are inactivated.Activated receptor tyrosine kinase receptors are internalized (recycled back into the system) in short time and are ultimately delivered to lysosomes, where they become work-adjacent to the catabolic acid hydrolases that partake in digestion.