The Resolution of Two Phases of Ferricyanide Reduction in Cultured Carrot Cells
Ferricyanide reductase activity is popularly determined over a relatively short period frequently as short as 10 mins. Over this time period the rate of ferricyanide reduction versus time is generally interpreted as being linear. By employing an amperometric method of ferricyanide measurement (a ferricyanide recycling method) (Chalmers et al 1984) rapid rates of electron transport may be followed over extended periods of time with no change in the redox potential of the bulk solution. A second advantage of this electrochemical method is that the output from the electrode (current) is directly proportional to the turnover of ferricyanide at any point in time rather than a measure of the remaining bulk solution ferricyanide concentration. The current-time profile is thus a direct representation of rate versus time. With an assay system showing these two features it becomes clear that in cultured carrot cells the rate of ferricyanide reduction with incubation time is not constant even over the initial relatively short time period, the first 10–15 mins, indeed the greatest rate of change in rate is observed at this stage.