Localization and Quantitative Determination of Ferredoxin-NADP+ Oxidoreductase, a Thylakoid-Bound Enzyme in the Cyanobacterium Anabaena sp. Strain 7119

Thylakoid membrane preparations obtained from mechanically disrupted (sonicated) cells of the cyanobacterium Anabaena sp. strain 7119 show a membrane-bound ferredoxin-NADP(+) oxidoreductase (EC 1.18.1.2) as determined either by specific antibodies or by using the ferredoxin-dependent NADPH-cytochrome c reductase activity, which is a specific test for this enzyme. However, in contrast with higher plant thylakoids, a low yield of the cyanobacterial reductase-only about 20% of the total amount of this protein estimated in whole cell homogenates-was obtained as a membrane-bound form when Mg(2+) was present during the disruption treatment. It is noteworthy that the addition of water-soluble nonionic polymers, namely polyethylene glycol and polyyinylpyrrolidone, dramatically increased the yield of the thylakoid-bound reductase, reaching values up to 80 to 85% of the total enzyme. Using these thylakoid membrane preparations, a quantitative determination of the reductase has been performed for the first time for cyanobacterial thylakoids. The value determined by immunoelectrophoresis-from 8 to 10 nanomoles per micromole of chlorophyll-is clearly higher than those reported for chloroplast thylakoids.