Discussion

The peroxydatic activity of haemoglobin in the presence of hydrogen peroxide catalyses the oxidation of TMB to a coloured product. Haemoglobin peroxidase has been termed a'pseudoperoxidase'7 because, unlike true peroxidases which exhibit specificity for phenols, erythrocytes contain a peroxidase (ery-throcyte glutathione peroxidase) specific for oxida-tion of reduced glutathione. This causes the in vitro detoxification of hydrogen peroxide. Glutathione peroxidase activity has been found to be associated with a relatively stable, nondialysible, heat-labile, intracellular component which can be separated from haemoglobin by gel filtration and ammonium sul-phate precipitation. The pH optimum of glutathione peroxidase has been shown to be pH 8-0 with negligible activities below pH 6.0. 8 Pretreatment of the fixed slides with resorcinol before staining with TMB and hydrogen peroxide inhibits myeloperoxidase staining. This increases specificity of the stain and re-duces error in enumeration of erythroid colonies. By omitting counter staining only erythroid colonies and precursors are stained.