부산대학교 도서관

1. In 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 NADP+ 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 Embden-Meyerhof pathway, in which the phosphofructokinase plays a key role. 4. The proportions of the two pathways at 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 without methylene blue. With increase 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. [ABSTRACT FROM AUTHOR]