PURIFICATION AND CHARACTERIZATION OF FERREDOXIN-NADP(-ALGA CHLORELLA-FUSCA() REDUCTASE FROM THE GREEN)

Ferredoxin-NADP(+) reductase (FNR, EC 1.18.1.2) from the green algae C hlorella fusca Shihira et Kraus 211-15, was purified to homogeneity. T he molecular mass was 36.8 kDa as determined by SDS-polyacrylamide gel electrophoresis. The enzyme exhibits the typical spectrum of a flavop rotein with an absorption maximum at 459 nm and an A(273/459) ratio of 7.2. It contains one mol of FAD per mol of protein and the calculated extinction coefficient is 9.8 mM cm(-1). Four different forms of the purified enzyme were detected by isoelectric focusing (pI between 5.4 and 5.9), even when protease inhibitors were used during the first ste ps of the purification. Kinetic parameters were determined for several FNR-catalyzed reactions. NADP(+) photoreduction gave comparable rates when either ferredoxin or flavodoxin was used.