Action spectra of photo phosphorylation 2. atp formation catalyzed by phenazine methosulfate suggesting the involvement of long wavelength pigment forms in the light harvesting process for photosystem ii and photosystem i

Van-Ginkel, G.; Hammans, J.W.K.

Photochemistry and Photobiology 31(4): 385-396

1980


ISSN/ISBN: 0031-8655
Accession: 004661481

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Abstract
Action spectra of phenazine methosulfate (PMS)-catalyzed photophosphorylation, forms at room temperature peaking at: 641.6; 650.3; 661.2; 669.8; 677.1; 684.0 and 690.6 nm. Comparison of our data with published data from low temperature absorption spectra indicates that lowering the temperature causes a decrease in halfwidth of the absorption bands but no significant change in peak position. The data support the hypothesis of French and coworkers that there are 4 universal forms of Chl a also at 25.degree. C. Careful investigation of data in literature does not give evidence that the pigment peaking at 641 nm is a 2nd form of Chl b, as is sometimes assumed. Because our action spectra show 2 small but distinct maxima at 703-705 and 718-720 nm when PS II is rate-limiting, we also measured action spectra of PS I (reduced PMS + DCMU) and PS II (ferricyanide-ions + 2,5-dibromo-3-methyl-6-isopropylbenzoquinone) separately. They show, in agreement with published data, that PS I is operating more efficiently in the spectral region 690-725 nm than PS II. The Chl form peaking at 690 nm is absent in the PS II action spectrum, whereas this curve has 2 small but distinct maxima around 703-705 and 718-720 nm, respectively, which are also present in the PS I action spectrum. It is suggested that light absorbed by these pigments can be transferred to either of the 2 photosystems, and not to PS I exclusively as is sometimes assumed.