Insertional inactivation of the psbO gene encoding the manganese stabilizing protein of photosystem II in the cyanobacterium Synechococcus PCC7942. Effect on photosynthetic water oxidation and L-amino acid oxidase activity.

A Synechococcus PCC7942 mutant in which the psbO gene was inactivated by insertion of a chloramphenicol interposon and which did not contain any detectable manganese stabilizing protein in immunoblot experiments, was constructed. Such a Synechococcus mutant was able to grow under photoautotrophic conditions. Isolated thylakoid membranes from the mutant required addition of CaCl2 and MnCl2 for photosynthetic O2 evolution, and the detectable L-amino acid oxidase activity in the isolated thylakoid membranes from the mutant was approximately four times higher than in wild-type thylakoids. The results are discussed with respect to our model suggesting that the water-oxidizing enzyme may have evolved from a flavoprotein with L-amino acid dehydrogenase/oxidase activity.