Processing of the D1 polypeptide of the photosystem II reaction centre and photoactivation of a low fluorescence mutant (LF‐1) of Scenedesmus obliquus

In the LF‐1 mutant of Scenedesmus obliquus, a failure to remove a C‐terminal extension from the D1 protein of photosystem II (PS II) is associated with the absence of a water‐splitting manganese complex. Treatment of LF‐1 thylakoids and PS II‐enriched membranes with a Triton X‐100 extract of wild‐type thylakoids results in a specific reduction in molecular mass of the LF‐1 D1 to the same value as that in wild‐type membranes. Water‐splitting activity can be photogenerated in these extract‐treated LF‐1 PS II‐enriched membranes, and in PS II membranes from dark‐grown wild‐type cells, but not in untreated LF‐1 membranes. The results indicate that LF‐1 cells lack the D1 processing protease, and that the presence of the D1 extension in LF‐1 is directly responsible for preventing assembly of the manganese complex.