Linnertz, H: 2'(3')-O-[N-[2-[3-[5-fluoresceinyl] thioureido] ethyl] carbamoyl] adenosine 5'-triphosphate and its Cr(H,2,O),4, and Co(NH,3,),4, complex derivatives are new fluorescent tools for labelling ATP binding sites of Na'+'/K'+|'-ATPase