LIGHT DARK REGULATION OF PHOTOSYNTHETIC ENZYMES WITHIN INTACT-CELLS OF THE CYANOBACTERIUM NOSTOC SP MAC

Light/dark regulation of several photosynthetic enzymes has been studied under near in vivo conditions using the cyanobacterium Nostoc sp. Mac. Cells were grown photoheterotrophically and rendered osmotically fragile by treatment with lysozyme. Treated cells evolved O2 during photosynthesis at 20-80% of the rate of control cells. Enzyme activities were measured following dilution of preilluminated cells into a hypotonic assay medium. Inhibitor studies using methyl viologen, N,N'-dicyclohexylcarbodiimide and triphenyl tin indicate that fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase, ribulose-5-phosphate kinase and NADP-linked glyceraldehyde 3-phosphate dehydrogenase are reversibly light-activated in vivo by the cyanobacterial thioredoxin system. In contrast, the protonmotive ATPase F0-F1-type ATPase appears to be fully active in both light- and dark-adapted cells at physiological temperatures, but is reversibly deactivated by cooling the cells on ice. No activity of NADP-linked malate dehydrogenase or glucose-6-phosphate dehydrogenase could be detected in these cells.