Fig. 4.

Inactivation of the flavodoxin reductase activity of FNR in the presence of various effectors. FNR (1 μM) alone and in the presence of flavodoxin, ferredoxin, FAD, or riboflavin (40 μM each) was reduced with NADPH (500 μM) in chilled 50 mM Bis-Tris Propane, 50 mM NaCl, pH 7.5, under argon. The initial flavodoxin reductase activity (dark bar) was determined by mixing with flavodoxin (100 μM) in a stopped-flow spectrophotometer at 37°C and following the formation of flavodoxin semiquinone at 580 nm. The samples were then incubated at 37°C for 30 min and the residual activity (light bar) was determined. Each bar represents the average of five trials.