We have studied the intracellular location of glycerol-3-phosphate oxidase and NAD+-linked glycerol-3-phosphate dehydrogenase, two enzymes involved in the very active dihydroxyacetone phosphate : glycerol-3-phosphate cycle in Trypanosoma brucei. Isopycnic centrifugation of a largegranule fraction resulted in a 10-20-fold purification of the oxidase and showed that the enzyme behaved like the mitochondrial ATPase, isocitrate dehydrogenase and the particulate malate dehydrogenase. The activity profiles of these four enzymes in sucrose gradients were identical with maximal activity at a density of 1.17 g/cm3. Electron micrographs of a fraction equilibrating at this density only showed mitochondrial profiles.The particle-bound NAD+-linked glycerol-3-phosphate dehydrogenase activity was found to band at a density of 1.23 g/cm3 in sucrose. A fraction equilibrating at this density was highly enriched in microbodies; it contained few mitochondrial profiles and less than 3 % of the specific oxidase activity of the mitochondrial fraction. Because of the absence of microbody markers in T. brucei we turned to the insect trypanosome Crithidia luciliae, which contains a high activity of the microbody marker catalase. In C. luciliae part of the catalase activity bands at the same density as the particle-bound NAD +-linked glycerol-3-phosphate dehydrogenase (@ = 1.26 g/cm3).From these results we conclude that in T. brucei bloodstream forms glycerol-3-phosphate oxidase is located in the mitochondrion and not in the microbodies, as proposed by a number of other investigators, and that the particle-bound NAD+-linked glycerol-3-phosphate dehydrogenase is located within the microbodies. It is likely that this highly active dehydrogenase plays an essential role in glycolysis.

The histoimmunological response of 8 individuals was studied longitudinally in relation to the development of experimental gingivitis during pregnancy and post-partum. At day 0 as well as at day 14 of experimental gingivitis the mean periodontal pocket bleeding index (PPBI) was higher during pregnancy than post-partum, whereas the amount of plaque that accumulated was similar. The number of CD1 positive cells (mainly Langerhans) in the oral epithelium was found to be higher during pregnancy. In the sulcular epithelium, however, the number of these cells tended to decrease during pregnancy as compared to post-partum. The number of CD4 positive cells in oral and sulcular epithelium was increased during pregnancy (P < 0.05). It was speculated that this increase in the number of CD4 positive cells is confined to the Th-1 subset, since the number of CD14 positive cells (mainly macrophages and granulocytes) together with the number of B cells was found to be decreased during pregnancy. Th-1 cells are known to be cytotoxic against these HLA class II antigen bearing cells. Consequently, cytotoxicity directed against B cells and macrophages may result in diminished immunoresponsiveness in pregnancy gingivitis.

In bacteria the exact location of a respiratory enzyme system comparable to that of the mitochondria of other cells has remained uncertain. On the one hand, the existence of particulate "bacterial mitochondria" has been advocated (Mudd); on the other hand, important enzymes of the respiratory chain were recovered in the cytoplasmic membranes associated with some granular material (Weibull). In order to gain insight into this question, sites of reducing activity were localized in thin sections of bacteria using the reduction of potassium tellurite as .an indicator. When this salt was added to the culture medium of Bacillus subtilis, it turned out that in this Gram~positive organism the reduced product is strictly bound at two sites, and that the plasma membrane does not materially gain in electron opacity through deposition of the reduced product. The reduction product is found on or in the membranes of particular organelles, which may possibly be regarded as the mitochondrial equivalents in Gram-positlve bacteria, and which are sometimes seen connected to the plasma membrane. The second location is in thin rod-like elements at the cell periphery, possibly the sites from which the flagella emerge.

In order to obtain information on the exact location of the respiratory enzyme chain in Gram-negative bacteria, an electron microscopic study was made of the sites of reducing activity of cells that had, in the living state, incorporated tellurite. In the test object Proteus vulgaris, the reduced tellurite was found to be deposited in bodies contiguous with the plasma membrane but different in structure from those described in the Gram-positive

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