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1. It has been shown that mixtures of normal and G-6-PD deficient nitrite-treated erythrocytes reduced methemoglobin at a rate considerably more rapid than that computed from their individual rates of methemoglobin reduction. 2. Differential agglutination studies demonstrated that when normal, methemoglobin-containing cells in such a mixture have reduced all of their methemoglobin, they facilitate methemoglobin reduction in G-6-PD deficient erythrocytes. 3. The same effect could be observed in other mixtures of cells, (e.g., normal with normal, G-6-PD deficient with G-6-PD deficient, etc.) and even with highly purified methemoglobin solutions. 4. This effect could be observed in the presence of methylene blue but not in the presence of another redox dye, Nile blue sulfate. 5. Lactate served as an effective substrate for methemoglobin reduction. Methemoglobin reduction by lactate was enhanced by methylene blue but not by Nile blue sulfate. 6. In mixtures of normal and G-6-PD deficient erythrocytes, no deficit in the rate of accumulation of lactate was found. This indicates that the mechanism of enhancement of methemoglobin reduction is not the diffusion of lactate from non-methemoglobin-containing cells to methemoglobin-containing cells. 7. It was demonstrated that leukomethylene blue could reduce highly purified solutions of methemoglobin in the absence of the enzyme "methemoglobin reductase." 8. The possible mechanism by which non-methemoglobin-containing cells may reduce methemoglobin in methemoglobin-containing cells is discussed. It seems most probable that leukomethylene blue is the mediator of the effect. This implies, contrary to earlier suggestions, that "methemoglobin reductase" acts prior to the reduction of methylene blue in the electron transport chain.

A simplified method is described for the determination of red cell ATP using the firefly lantern extract method. Variables investigated include the effect of the time of reading, dilution of firefly extract and the effective range of the method. Excellent recoveries were obtained. Optimal extraction of ATP from red cells was achieved with a hypotonic buffer at pH 9.2. The method could be used with acid-citrate-dextrose, heparin or EDTA as an anticoagulant. The method was found to be highly specific when the nucleotides found in normal human blood were investigated; only adenosine diphosphate and guanosine triphosphate gave slight readings, neither of which would significantly affect ATP determinations of human blood. Normal human values were found to be 5.45 µmoles of ATP/Gm. of hemoglobin or 1.83 µmoles/ml. red cells in heparinized blood samples. This method is believed to be more rapid, more reproducible and more accurate than any previously described method of ATP determination.

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