Properties of the glyceraldehyde-3-P dehydrogenase in heterocysts and vegetative cells of cyanobacteria

Glyceraldehyde-3-P dehydrogenase (GAPDH) in heterocysts and vegetative cells of 3 N2-fixing cyanobacteria was found to utilize both NAD(+)-ion and NADP(+)-ion. The enzyme activity was enhanced by thiols (glutathione, reduced lipoic acid and dithiothreitol). GADPDH of the 3 cyanobacterial species was not activated by thioredoxin. Heterocysts have now been shown to possess all the enzymes of glycolysis and the tricarboxylic acid cycle to convert glyderaldehyde-3-phosphate (GAP) to oxoglutarate and glutamate. The GADPDH reaction is a major source for the generation of NADH, which is oxidized by a thylakoidbound NADP:plastoquinone oxidoreductase in heterocysts. (IFU)