The regulatory role of photosystem II photoinactivation and de novo protein synthesis in the degradation and exchange of two forms of the D1 protein in the cyanobacterium Synechococcus PCC 7942

✍ Scribed by J. Komenda; M. Koblížek; J. Masojídek

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 636 KB
• Volume: 48
• Category: Article
• ISSN: 1011-1344
• DOI: 10.1016/s1011-1344(99)00025-1

✦ Synopsis

After exposure of cells of the cyanobacterium Synechococcus PCC 7942 to increased irradiance, there is a good correlation between the rate of exchange of the 'low-light' form DI:I for the 'high-light' form D1:2, and the rate of photosystem II photoinactivation (PSIIPI) assessed in chloramphenicol ( CAP)-treated cells. This result indicates that PSIIPI triggers the exchange of D 1:1 for D 1:2. On the other hand, the reverse exchange of D1:2 for D1:1 after return of the cells to low irradiance is apparently independent of PSIIPI. The D1:2 degradation is partially inhibited by the protease inhibitor Pefabloc, suggesting the role of a serine protease in this process. The degradation of both D 1:1 under high irradiance and D 1:2 under low irradiance is slowed down in the presence of CAP, confirming previous results obtained with other cyanobacterial strains. A comparison of the turnover rates of the D 1 forms under high irradiance shows that the radiolabelled D 1:2 turns over significantly faster than D 1:1. The presence of D 1:2 in the membrane therefore improves the protection of PSII against photodamage and this can be the primary reason for the preferential synthesis of this form under high irradiance.