Increases in peroxide formation by the Photosystem II oxygen evolving reactions upon removal of the extrinsic 16, 22 and 33 kDa proteins are reversed by CaCl2addition
✍ Scribed by Warwick Hillier; Tom Wydrzynski
- Publisher
- Springer
- Year
- 1993
- Tongue
- English
- Weight
- 766 KB
- Volume
- 38
- Category
- Article
- ISSN
- 0166-8595
No coin nor oath required. For personal study only.
✦ Synopsis
This communication introduces a new spectrophotometric assay for the detection of peroxide generated by Photosystem II (PS II) under steady state illumination in the presence of an electron acceptor. The assay is based on the formation of an indamine dye in a horseradish peroxidase coupled reaction between 3-(dimethylamino)benzoic acid and 3-methyl-2-benzothiazolinone hydrazone. Using this assay, we found that as the 02 evolution activity of PS II-enriched membrane fragments is decreased by treatments which cause the dissociation of the 33 and/or 23 and 16 kDa extrinsic proteins (i.e., CaC12-washing, NaCl-washing, lauroylcholine-treatment and ethylene glycol-treatment), light-induced peroxide formation increases. Both the losses of 02 evolution and increases in peroxide formation seen under these conditions are reversed by CaC12 addition, indicating that the two activities originate from the water-splitting site. However, the increased rates of peroxide formation do not quantitatively match the losses in O z evolution activity. We suggest that a rapid consumption of the peroxide takes place via a catalase/peroxidase activity at the watersplitting site which competes with both the 02 evolution and peroxide formation reactions. The observed peroxide formation is interpreted as arising from enhanced water accessibility to the catalytic site upon perturbation of the extrinsic proteins which then leads to altemate water oxidation side reactions.