Cytochemical localization of peroxidase activity in the developing erythrocyte

Peroxidase activity, demonstrated with diaminobenzidine as the electron donor according to the method of Graham and Karnovsky, was used as a cytochemical marker in a study of developing erythrocytes in guinea pig and rabbit bone marrow. Peroxidase activity was deposited diffusely in the cytoplasm and nuclear matrix of developing cells and was thought to represent hemoglobin, which others have shown by independent criteria to have a similar distribution. Diffuse localization was first observed in erythroblasts and at all subsequent stages of development. Another finding was the significant particulate localization of peroxidase activity apparently associated with cytoplasmic ribosomes and nuclear particles of immature erythrocytes. This activity differentiated the most primitive erythroid precursors from hemocytoblasts of other marrow cell lines, a distinction impossible by strictly morphologic criteria. Particulate peroxidase localization was identified in erythroid hemocytoblasts, erythroblasts, normoblasts and reticulocytes but not in mature erythrocytes. The nature of the particle-associated peroxidase activity was not determined with certainty. However, it could not be differentiated from the diffuse activity, thought to reflect hemoglobin, by several inhibitors and could not be attributed to erythrocyte catalase. The possibility is therefore raised that this activity represents hemoglobin, newly assembled either on or immediately adjacent to nuclear particles and cytoplasmic ribosomes.