Slow oxygen release on the first two flashes in chemically stressed Photosystem II membrane fragments results from hydrogen peroxide oxidation
✍ Scribed by Shinichi Taoka; Paul A. Jursinic; Michael Seibert
- Book ID
- 104622414
- Publisher
- Springer
- Year
- 1993
- Tongue
- English
- Weight
- 598 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0166-8595
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✦ Synopsis
Flash-induced amperometric signals were measured with a Joliot-type 02 rate electrode in spinach Photosystem II (PS II) membrane fragments exposed to very low concentrations of added hydroxylamine or hydrogen peroxide. In both cases 'anomalous 02 signals' were observed on the first two flashes, and oscillating four-flash patterns were observed on subsequent flashes. The anomalous signals were eliminated in the presence of catalase but not EDTA. The rise times of the O2-release kinetics associated with the anomalous signals were slow (ca. 20 ms with NH2OH and ca. 120 ms with H202) compared to the kinetics of 02 release on subsequent flashes and in control membranes (3-6 ms). It is proposed that when the intact PS II O2-evolving complex is perturbed with small concentrations of added reductant, H202 can gain access and bind to the complex. Bound H202 can then reduce lower S states in some centers leading to anomalous 02 signals on the first two flashes. A model is presented to explain both types of anomalous 02 production. Oxygen observed on the third and subsequent flashes is due to the normal photosynthetic O2-evolution process arising from the S3-state. Anomalous 02 production could be a protective mechanism in PS II centers subjected to stress conditions.