Kinetics of photocurrent induction by a thylakoid containing electrochemical cell

• Published in: Bioelectrochemistry and Bioenergetics 1989, Vol.22 (2), p.145-158
• Main Authors: Mimeault, Murielle, Carpentier, Robert
• Format: Article
• Language: English
• ISSN: 0302-4598
• DOI: 10.1016/0302-4598(89)80047-9

The induction kinetics of photocurrent generation by an electrochemical cell containing thylakoid membranes were studied in order to identify the parameters which limit the photocurrent induction. It was demonstrated that both 2,5-dichlorobenzoquinone and dissolved oxygen can act as electroactive mediators between the negatively charged species formed in the thylakoid membrane upon illumination, and the working electrode kept under a positive imposed potential. Because the photocurrent depended upon the diffusion of electroactive species, its induction rate varied with the temperature and with the viscosity of the electrolytic medium. The induction rate constant also varied with the ratio between reduced and oxidized acceptor molecules and was therefore dependent on the thylakoid membrane activity. The photocurrent produced was related to the electron transfer rate of the thylakoid membranes in the bulk of the cell. Thus, the electrochemical cell provided an acurate methodology for electron transfer measurement, even when a very limited amount of material (e.g. 1 μg on a chlorophyll basis) was available. The monitoring of photocurrents with oxygen as an acceptor also offered a unique way of evaluating photosystem I activity with photosystem II as a donor, because oxygen evolution did not interfere with the photocurrent measurements, as is the case when oxygen uptake is monitored.