Fructose-stimulated ferricyanide reduction by intact blue-green algae

As reported in the literature, ferricyanide reduction of blue-green algal cells in the dark is linked to respiratory electron transport. This study has not verified this hypothesis.There was no concurrent activity of ferricyanide reduction by intact cells withrespiratory oxygen uptake. It was found light-independent, showing little KCN-inhibition, but was strongly CCCP-sensitive. CCCP inhibition was reversed by KCN. - Both, respiration and ferricyanide reduction were stimulated by fructose which was actively accumulated by the cells (the apparent K_m was 20 μM). Ferricyanide reduction was more sensitive towards dark starvation than respiration. Based on these data it is suggested that ferricyanide reduction and cyanide-sensitive respiration are parts of different electron-transport processes, competing for reduction equivalents originating from the same (endogenous) carbon pool.