Lead-Adenosine Triphosphate Complexes in Adenosine Triphosphatase Histochemistry

Chelation of lead by adenosine triphosphate (ATP) and its consequences for adenosine triphosphatase histochemistry were examined. The formation constant of lead-ATP chelates was found by two methods to be 4.6-4.7 x 10 4 . The characteristics of enzyme inhibition by lead were consistent with the predicted effects of lead-ATP chelation. Inhibition was overcome by increasing ATP concentrations. With the adenosine triphosphatase from liver microsomes, which retained some activity in the presence of 4 mM Pb(NO 3 ) 2 , substrate inhibition disappeared and increased MgCl 2 was required for optimal activity. Increased solubility of lead phosphate was observed in the presence of increasing quantities of ATP in a manner predictable from lead-ATP chelation.