Methemoglobin reduction

Finally, the methemoglobin reduction test may be briefly mentioned. The test has been developed for the detection of primaquine sensitivity and depends on the function of the G-6-PDH system. Its principle consists in the oxidation of Hb to MHb by sodium nitrite and the subsequent enzymatic reduction to Hb in presence of methylene blue. The activity of this system can be followed easily by observation of alterations in color after an incubation period or by means of MHb determinations before and after this period (B18). 

Methylene blue and other reducible dyes were shown to enhance the activity of NADPHa-linked MHbR (K8, K9). This is confirmed by the finding that intravenous injections of methylene blue in methemo-globinemic patients result in a striking decrease of MHb levels (e.g., B14, K9, K10). This seems to be paradoxical, since methylene blue is capable of reacting with Hb with formation of MHb, but the dye reacts much more effectively as an artificial electron carrier in the NADPH2-MHbR Systran (B14). It has been stated (K10) that methemoglobin reduction is associated with the formation of pyruvate in equivalent amounts, but that in reactions accelerated by reducible dyes no correlation between pyruvate formation and MHb reduction could be found. 

B18. Brewer, G. J., Tarlov, A. R., and Alving, A. S., Methemoglobin reduction test Bud. World Health Organization 22, 633-644 (I960). 

Takeoka S, Ohgushi T, Sakai H, et al. Construction of artificial methemoglobin reduction systems in Hb vesicles. Artif Cells Blood Substit Immobil Biotechnol 1997 25 31. 

A number of these enzymes are expressed in other tissues as well but cause a notable deficiency predominantly in red blood cells because of the life span of the erythrocyte after the loss of protein synthesis. Once an enzyme is degraded or otherwise becomes nonfunctional, it cannot be replaced by new or other compensating proteins because of the lack of nucleus, mitochondria, ribosomes, and other cell organelles in mature red cells. Disorders have been described in the EMP, HMP, Rapoport-Luebering cycle, the glutathione pathway (Figure 21-9), purine-pyrimidine metabolism and methemoglobin reduction. 

Web site http //www.nlm.nth.gov/medlineplus/ency/article/003363.htm Methemoglobin reduction... 

Catalysis of Methemoglobin Reduction Donald E. Hultquist, Lucy Jean Sannes, and David A. Juckett... 

Tomoda, A., Matsukawa, S., Takeshita, M, and Yoneyama, Y., 1976, Effect of organic phosphates on methemoglobin reduction by ascorbic acid, /. Biol. Chem. 251 1794. 

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