Simultaneous occurrence of two different glyceraldehyde-3-phosphate dehydrogenases in heterocystous N-2-fixing cyanobacteria

Enzyme activity determinations and Western and Northern blot analyses have shown the presence of two catalytically different glyceraldehyde-3-phosphat e dehydrogenases (GAPDH) in both vegetative cells and heterocysts of severa l N-2-fixing Anabaena strains: (a) the gap2-encoded NAD(P)-dependent GAPDH2 (EC 1.2.1.59), the enzyme involved in the photosynthetic carbon assimilati on pathway, which is present at higher levels in vegetative cells, and (b) the gap3-encoded NAD-dependent GAPDH3 (EC 1.2.1.12), presumably involved in carbohydrate anabolism and catabolism, which is the predominant GAPDH in h eterocysts, In contrast, the gap1-encoded GAPDH1, which is the other NAD-de pendent cyanobacterial GAPDH, is virtually absent in both cell types. These findings are discussed in the context of carbon metabolism of heterocystou s N-2-fixing cyanobacteria, (C) 2001 Academic Press.