Regulierende Faktoren der Methylenblaukatalyse in Erythrocyten

Abstract

1. I n erythrocytes of man and rabbits methylene blue catalysis is limited by the following factors at the pH optimum 7.5; primarily by the cellular concentration of NADP+, next by that of glucose-6-P. Possible further limiting steps are glucose-6-phosphate dehydrogenase, phosphogluconate dehydrogenase and reduced-NADP dehydrogenase.2. Calculation of the intracellular NADPf concentration with the two-substrate equation for the glucose-6-phosphate dehydrogenase-reaction does not yield reasonable results. The existence of inhibiting factors of the methylene blue catalysis is postulated. Their amount is presumably lower in intact cells as compared with hemolysates.3. There is no pH dependence of the glucose-6-P concentration in presence of methylene blue. There exists a competition between the oxidative pentose-phosphate-pathway and the EmbdenMeyerhof pathway, in which the phosphofructokinase plays a key role.4. The proportions of the two pathways a t different pH values are calculated from data on oxygen and glucose consumption. At pH values below 7.6 glucose is utilized practically exclusively via the oxidative pentose phosphate pathway, whereas the Embden-Meyerhof pathway is inhibited. At pH 8.2 the participation of the oxidative pentose-phosphate pathway amounts to 40°/, of the total glucose utilization, while the Embden-Meyerhof pathway is little if any reduced as compared to cells withouth methylene blue.5 . With increased degree of oxidation of the pyridine nucleotides there occur decreases in the levels of hexose-and triose-phosphates. With these changes and the decreased flow to lactate an increased formation of 2,3-diphosphoglycerate occurs.

Hexose monophosphate shunt activity in erythrocytes related to cell age

“…The basal HMP-shunt activities of the total population measured with I4C-1-labelled glucose are higher than reported by Magnani et al (22) and Davidson & Tanaka (18), but comparable with the results of Trotta et al (23). The MB-stimulated HMP-shunt activity of the total population is more than 2-fold higher than reported by Magnani (22) or Davidson & Tanaka (1 8), but about equal to the values found by Rogias et a1 (24) and Albrecht et al (25).…”

Genetic variants of human erythrocyte glucose 6-phosphate dehydrogenase. II. In vitro and in vivo function of the A- variant

“…Under normal conditions the rate of operation of the pentose phosphate pathway is limited by both the concentration of NADP+ and that of glucose 6-phosphate dehydrogenase (Roigas et al, 1970). The enzyme under physiological conditions can be estimated in two different ways, (a) C02 production is measured and is related to maximal C02 production (Table I).…”

Interrelationship and control of glucose metabolism and lipogenesis in isolated fat-cells. Control of pentose phosphate-cycle activity by cellular requirement for reduced nicotinamide adenine dinucleotide phosphate

“…There are numerous reports of a stimulation of the pentose phosphate cycle in various tissues by the addition of electron acceptors such as Methylene Blue or phenazine methosulphate, suggesting that the flux via this pathway might be controlled by mass action with respect to the NADP+/NADPH ratio (Brin & Yonemoto, 1958;Holzer & Witt, 1958;Roigas et al, 1970;Brand et al, 1970). No direct evidence for a control of the pentose phosphate cycle by an NADPH-requiring biosynthetic process has been presented so far.…”