Abstract
Data are presented which show that the reaction product formed in adenosine triphosphatase cytochemical procedures is not simple lead phosphate. Both by chemical and electron microscope autoradiographic techniques, reaction product was found to contain nucleotide as well as lead and phosphate. Nearly equimolar quantities of nucleotide and phosphate are present in tissue incubated in a standard Wachstein-Meisel medium. Electron microscope autoradiographs demonstrate that nucleotide is uniformly associated with adenosine triphosphatase reaction product, regardless of its cellular distribution. In vitro studies of the interaction of nucleotide with lead and phosphate are also presented. The relationship of these observations to the validity of lead-salt cytochemical procedures is discussed.