[Ultracytochemical demonstration of enzymes by reduction of potassium hexacyanoferrate (III). I. A method for demonstration of xanthine oxidase].

Xanthine oxidase is a flavoprotein which directly catalyses the oxidation of xanthine and hypoxanthine by oxygen or by potassium ferricyanide as an artificial acceptor of protons. In doing so, the potassium ferricyanide is reduced into potassium ferrocyanide which in the presence of manganese(II)ions leads to the manganese(II)ferrocyanide which is insoluble in water and in organic solvents. The latter is deposited on the areas with enzyme activity and marks them under the electron microscope. After the detection of the xanthine oxidase in rat liver on ultrathin non-contrasted sections, it was observed that the fine granular reaction product was deposited only on the peroxisomes of the hepatocytes. A greater quantity of the reaction product is deposited on the outer membrane and the matrix and a smaller one on the nucleoid of these cell organelles. No deposition of the reaction product was observed on the other cell structures. The method can be used for the study of purine metabolism on the cellular level as well as for the specific ultracytochemical detection of the peroxisomes.