DIFFERENTIAL-EFFECTS OF FORMATE IN SINGLE AND DOUBLE MUTANTS OF D-1 IN SYNECHOCYSTIS SP PCC-6714

Using several single and double mutants in the d-e interhelical loop o f D-1 protein in Synechocystis sp. PCC 6714, we have shown that a diff erential sensitivity of formate inhibition on the acceptor side of Pho tosystem II occurs in the following order: S264A-F255L > S264A = N266T > N266T-S264A > F255L = N266D = WT much greater than N266T-A251V = A2 51V. On the basis of the absence of additivity of the effects between single and double mutants, it is concluded that the couples S264 and N 266, N266 and A251, and S264 and F255 interact with each other in form ate binding. It is considered highly likely that these effects are due to the modification, to some extent, of the overall conformation of t he D-1 protein which, in turn, modifies the formate/bicarbonate bindin g at its site in the same protein.