Shigeki Minakami

The hydrogen ion concentrations and erythrocyte glycolysis

Recently several reports appeared on the control of glycolysis in living cells, notably tumor cells (Wu, 1964) and cerebral tissues (Lowry et al. 1964). In these studies, the glycolytic intermediates of the cells are assayed enzymatically and the controlling points are analyzed by the “crossover theorem” of Chance et aL(1958). Erythrocytes seemed to be one of the most suitable cells for this kind of analysis, as glycolysis is predominant compared to other metabolic activities. The pattern of glycolytic enzymes are systematically studied by Chapman et al. (1962) and some of the intermediates were assayed chromatographically by Bartlett (1959) and Yoshikawa et aL(l960). Hexokinase has been considered as the rate-limiting step in the glycolytic chain of the cells by several investigators (Rapoport et al.,1961, Chapman et al., 1962, Rose and O’Connell, 1964), as the hexokinase activity is the lowest in the glycolytic enzymes and glycolytic rates of the red cells are found to be parallel to those of hexokinase in several conditions, e.g. aging, storage and in different species of animals. The optimum pH for the glycolysis of the cells lies at pH 8.1, which coincides with those of hexokinase. In this paper, the contents of glycolytic intermediates of human erythrocytes except 1,3diphosphoglycerate are reported, especially in relation to the

Xylit als Substrat für Methämoglobinreduktion in roten Blutkörperchen

SummaryThe rate of reduction of methemoglobin in fresh erythrocytes in a glucose medium, ranging in concentration from 50–500 mM glucose, is constant; however, in a xylit medium the reduction is dependent upon the concentration of the xylit. The highest rate appears at a substrate concentration of 200 mM xylit. Upon addition of glucose, erythrocytes, which were stored in an acid-citrate-dextrose medium for more than five weeks, barely reduce methemoglobin, whereas upon addition of xylit they still reduce methemoglobin well.ZusammenfassungDie Geschwindigkeit der Reduktion von Methämoglobin in frischen Erythrocyten ist im Glucosemedium im Konzentrationsbereich von 50–500 mM Glucose konstant, im Xylitmedium jedoch von der Konzentration des Xylit abhängig. Die größte Geschwindigkeit tritt bei einer Substratkonzentration von 200 mM Xylit auf. Erythrocyten, die mehr als 5 Wochen in Citronensäure-Dextrose-Medium aufbewahrt wurden, können bei Zugabe von Glucose kaum, bei Zugabe von Xylit noch gut Methämoglobin reduzieren.

Utilization of Xylitol in Human Erythrocytes

Mature human erythrocytes synthesize no DNA, RNA, heme or protein. They possess no citric acid cycle or electron transfer system, and obtain the energy mainly from carbohydrate metabolism through the Embden-Meyerhof and Warburg-Dickens pathways.