Reconstitution and identification of component(s) functioning in cyclic electron transport in a cell-free system in Synechocystis sp. PCC 6803.

Abstract

Cyanobacteria possess a hight activity of cyclic electron transport. The several pathways have been proposed, but they are not established. To identify the possible component(s) of the pathway in cyanobacteria, we tried to reconstruct the cyclic electron transport in a cell-free system. Thylakoids with high activities were isolated from Synechocystis 6803 cells by an improved method. In the presence of DCMU, the activity monitored by P700⁺ rereduction was reconsituted by addition of soluble fraction. To identify the component(s), the soluble fraction was fractionated. Ferredoxin was found to be an important component. The activity was successfully reconstituted by addition of Fd and NADPH or NADH. In the case of NADH, rotenone inhibited the rereduction of P700⁺. This suggests that NAD(P)H dehydrogenase complex 1 is the main pathway when NADH is an electron donor. The missing subunits of NDH-1 which act as electron imput device are now under investigation.