Abstract
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 104. 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 4mM Pb(NO3)2, substrate inhibition disappeared and increased MgCl2 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.