Zweiter Internationaler Kongreß für Histo- und Cytochemie / Second International Congress of Histo- and Cytochemistry / Deuxième Congrès International d’Histochimie et de Cytochimie pp 152-156 | Cite as
The granules of the eosinophil leukocytes of the rat give an intense benzidine-peroxidase reaction. Pretreatment with phosphotungstic or phosphomolybdic acid partly inhibits the reaction: instead of the end product of the reaction, i.e., “benzidine-brown”, a quinonediimine-derivative, the granules appear in bluish-grey colour, suggesting that in intermediary product, “benzidin-blue” is formed. — Electronmicroscopical observations show that both benzidine-peroxidase activity and phosphotungstic acid staining are localized to the outer part of the granules, the externum. The enzyme myeloperoxidase with its high isoelectric point (pH 10–11) is responsible for the peroxidase reaction and may be the cause of the phosphotungstic acid staining of the granules. The partial inhibition of the reaction in the pretreated granules is probably connected with local acidic medium produced by the free radicals of phosphotungstic acid. These stabilize the benzidine-peroxidase reaction in the stage of “benzidine-blue”, a phenomenon which may be observed light microscopically during benzidine-peroxidase reaction, when the medium is acidified.
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