Hi there,

AS RBC are devoided of any mitochondria, LDH is in charge there to recycle NADH into NAD+ in order to allow glycolysis to function as a source of ATP.

Dehydrogenases, in additon to LDH,  are present in red blood cells. Although in some cases the physiologically relevant reaction might convert NAD to NADH, if the reaction is run in the reverse direction it should be able to convert NADH to NAD.

sorbitol dehydrogenase

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC498353/

glyceraldehyde-3-phosphate dehydrogenase

http://www.ncbi.nlm.nih.gov/pubmed/146525

Thanks for your answers folks! I had one more question. The enzyme NADH Cytochrome b5 reductase uses reducing equivalents from NADH to convert methemoglobin to hemoglobin. Methemoglobin is a form of hemoglobin with the core iron in the form of Ferric ion. It is generated during physiological conditions, and converted back to Ferrous ions by the above mentioned enzyme. To determine the activity of this enzyme, normal hemoglobin in hemolysate is converted to ferrihemoglobin by treatment with ferricyanide. NADH is supplied to this reaction mixture and enzyme activity is detected by monitoring decrease in absorbance of NADH at 340 nm. I was wondering if this reaction can be regarded as specific for NADH Cytochrome b5 reductase and could it be used to detect enzyme activity on a routine basis?

If you are using whole cells or a subcellular preparation rather than a purified enzyme, there is the risk that some other enzyme activity also present in the preparation may be catalyzing NADH oxidation. You can test for this background activity if you have a specific inhibitor of NADH cytochrome b5 reductase, or by omitting the methemoglobin substrate, and measuring the rate of absorbance decrease at 340 nm.

Thank you Adam, that was really helpful!!