Abstract
The specificity of Nitro BT as an electron acceptor for the intracellular localizations of succinic dehydrogenase in mammalian blood cells was investigated. Imprints of mouse spleen were fixed either by immersion in acetone or formol calcium under varying conditions of time and temperature or by freezing in cold isopentane. The incubation mixture used for the detection of enzyme activity contained succinate, Nitro BT, amytal, and phosphate buffer (pH 7.4). By comparison of the intensity and site of formazan production in imprints prepared under varying conditions of fixation, it was found that specific intracellular localization of succinic dehydrogenase occurred only in cells fixed in formol calcium prior to, or after incubation with Nitro BT. Using this fixation method, succinic dehydrogenase was detected in the hemocytoblast, lymphocyte, myelocyte, and megakaryocyte. In all these cell types the enzyme was confined exclusively to the mitochondria. Only slight activity was observed in occasional metamyelocytes and none in any of the mature segmented forms. Imprint cells fixed in formol calcium failed to exhibit endogenous enzyme activity when succinate was omitted from the incubation medium (control series). It was also shown that reduction of Nitro BT was inhibited completely in the presence of 6 mM malonic acid (inhibition series) and that this inhibition was reversible in the presence of excess succinate (reversal series). The results of this study are discussed in terms of their possible significance in the differentiation process leading to formation of the mature granulocyte. On the basis of our findings and other information in the literature concerning modifications in fine structure of the mitochondria during blood cell maturation, it was suggested that cytogenesis of the granulocyte is associated with a progressive loss in oxidative enzyme activity and that oxidation reactions in the mature granulocyte may be mediated, for the most part, by glycolysis.
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