Determination of the PS I content of PS II core preparations using selective emission: a new emission of PS II at 780nm.
Routinely prepared PS II core samples are often contaminated by a significant (~1-5%) fraction of PS I, as well as related proteins. This contamination is of little importance in many experiments, but masks the optical behaviour of the deep red state in PS II, which absorbs in the same spectral range (700-730nm) as PS I (Hughes et al. 2006). When contamination levels are less than ~1%, it becomes difficult to quantify the PS I related components by gel-based, chromatographic, circular dichroism or EPR techniques. We have developed a fluorescence-based technique, taking advantage of the distinctively different low-temperature emission characteristics of PS II and PS I when excited near 700nm. The approach has the advantage of providing the relative concentration of the two photosystems in a single spectral measurement. A sensitivity limit of 0.01% PS I (or better) can be achieved. The procedure is applied to PS II core preparations from spinach and Thermosynechococcus vulcanus. Measurements made of T. vulcanus PS II preparations prepared by re-dissolving crystallised material indicate a low but measurable PS I related content. The analysis provides strong evidence for a previously unreported fluorescence of PS II cores peaking near 780nm. The excitation dependence of this emission as well as its appearance in both low PS I cyanobacterial and plant based PS II core preparations suggests its association with the deep red state of PS II.
Research School of Chemistry, Australian National University, Canberra, Australia.
Jennifer
J
Morton
Jeremy
J
Hall
Paul
P
Smith
Fusamichi
F
Akita
Faisal Hammad Mekky
FH
Koua
Jian-Ren
JR
Shen
Elmars
E
Krausz
D000042:Absorption; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D002942:Circular Dichroism; D000458:Cyanobacteria / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005453:Fluorescence; D007700:Kinetics; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D018724:Spinacia oleracea / Q000737:chemistry / Q000502:physiology; D013696:Temperature
D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll
Fluorescence; Fluorescence line-narrowing; Photosystem I; Photosystem II; Spectral hole-burning