Fine structural and cytochemical identification of microperoxisomes in developing human erythrocytic cells

An alkaline diaminobenzidine (DAB) medium has been used to identify peroxidase activity in small granules (0.09 to 0.2 mu in diameter) present in all forms of maturing erythrocytic cells with the exception of erythrocytes. These granules, which were more frequent in proerythroblasts (from two to seven by thin section), were distinct from pleomorphic granules present in the close proximity to the Golgi apparatus. They were also distinct from ferritin molecules which were seen as aggregates in siderosomes of polychromatophilic erythroblasts. They often appeared in close association with the smooth membrane of the nuclear envelope. Optimal conditions for the visualization of these granules by incubation in alkaline DAB were obtained when the peroxidase activity of hemoglobin was reduced by addition of low concentrations of potassium cyanide. Lack of hydrogen peroxide in the incubation media completely inhibited the staining reaction of hemoglobin, while the positive reaction persisted in the granules. Aminotriazole in the incubation media prevented the staining of these organelles. These findings suggest that small granules seen in maturing erythroblasts contain catalase and that they correspond to microperoxisomes described in other tissues. The mechanism of their disappearance during reticulocyte maturation is unknown. The relationship between particulate catalase of erythroblasts and soluble erythrocytic catalase has not been elucidated.