Adenosine deaminase activity associated with phagocytic vacuoles. Cytochemical demonstration by electron microscopy

Adenosine deaminase activity has been localized within the cell membrane and it surrounds phagocytic vacuoles in mouse macrophages. Adenosine deaminase is thus strategically located to direct metabolic flux through the enzymes of the purine catabolic pathway. Xanthine oxidase, a key enzyme of this pathway, produces superoxide during its reaction with its substrates. Enzyme activity was visualized for electron microscopy by means of hydrolysis of 6-Chloropurine ribonucleoside to produce Cl-, which is precipitated with Ag+. The latter is converted into Ag0 by light, and the resulting deposit is visualized with the electron microscope.