Resting rates of Rana ridibunda erythrocyte glucose consumption and 14CO2 production from 1-14C-glucose were found to be significantly lower than the respective values in human erythrocytes. 2. In the presence of 1-14C-glucose Methylene Blue stimulated 14CO2 production 7-fold, while in the presence of 6-14C-glucose Methylene Blue stimulated 14CO2 production 1.2-fold. 3. The Km of G-6-PD for G-6-P and NADP were 29 and 12 microM, respectively while the Km of 6-PGD for 6-PG and NADP were 83 and 32 microM, respectively. The Ki of G-6-PD and 6-PGD for NADPH were 80 and 12 microM, respectively. 4. Excess amounts of NADP resulted in a significant decrease of 14CO2 production from 1-14C-glucose in total haemolysates. 5. ATP, ADP and fructose diphosphate inhibited both G-6-PD and 6-PGD, the latter being more sensitive than G-6-PD to their inhibitory effect, 2,3-DPG and reduced and oxidized glutathione showed a marked inhibitory effect on 6-PGD, while the phosphorylated trioses inhibited only G-6-PD. 6. Physiological concentrations of oxidized glutathione decreased the inhibition exercised by NADPH on G-6-PD. 7. The possible role of the two dehydrogenases in the regulation of the HMS is discussed.
