Key cofactors of photosystem II cores from four organisms identified by 1.7-K absorption, CD and MCD.
Active Photosystem II (PS II) cores were prepared from spinach, pea, Synechocystis PCC 6803, and Thermosynechococcus vulcanus, the latter of which has been structurally determined [Kamiya and Shen (2003) Proc Natl Acad Sci USA 100: 98-103]. Electrochromic shifts resulting from QA reduction by 1.7-K illumination were recorded, and the Qx and Qy absorption bands of the redox-active pheophytin a thus identified in the different organisms. The Qx transition is approximately 3 nm (100 cm-1) to higher energy in cyanobacteria than in the plants. The predominant Qy shift appears in the range 683-686 nm depending on species, and does not appear to have a systematic shift. Low-temperature absorption, circular dichroism (CD) and magnetic circular dichroism (MCD) spectra of the chlorophyll Qy region are very similar in spinach and pea, but vary in cyanobacteria. We assigned CP43 and CP47 trap-chlorophyll absorption features in all species, as well as a P680 transition. Each absorption identified has an area of one chlorophyll a. The MCD deficit, introduced previously for spinach as an indicator of P680 activity, occurs in the same spectral region and has the same area in all species, pointing to a robustness of this as a signature for P680. MCD and CD characteristics point towards a significant variance in P680 structure between cyanobacteria, thermophilic cyanobacteria, and higher plants.
Arsköld
Sindra Peterson
SP
Research School of Chemistry, The Australian National University, Canberra, ACT 0200, Australia. sindra.peterson_arskold@biokem.lu.se
Smith
Paul J
PJ
Shen
Jian-Ren
JR
Pace
Ron J
RJ
Krausz
Elmars
E
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D000458:Cyanobacteria / Q000737:chemistry* / Q000378:metabolism; D004735:Energy Transfer; D018532:Pisum sativum / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D013045:Species Specificity; D013054:Spectrophotometry, Atomic; D018724:Spinacia oleracea / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll