Abstract:
:In high light conditions, cyanobacteria dissipate excess absorbed energy as heat in the light-harvesting phycobilisomes (PBs) to protect the photosynthetic system against photodamage. This process requires the binding of the red active form of the Orange Carotenoid Protein (OCP(r)), which can effectively quench the excited state of one of the allophycocyanin bilins. Recently, an in vitro reconstitution system was developed using isolated OCP and isolated PBs from Synechocystis PCC 6803. Here we have used spectrally resolved picosecond fluorescence to study wild-type and two mutated PBs. The results demonstrate that the quenching for all types of PBs takes place on an allophycocyanin bilin emitting at 660 nm (APC(Q)(660)) with a molecular quenching rate that is faster than (1 ps)(-1). Moreover, it is concluded that both the mechanism and the site of quenching are the same in vitro and in vivo. Thus, utilization of the in vitro system should make it possible in the future to elucidate whether the quenching is caused by charge transfer between APC(Q)(660) and OCP or by excitation energy transfer from APC(Q)(660) to the S(1) state of the carotenoid--a distinction that is very hard, if not impossible, to make in vivo.
journal_name
Biophys Jjournal_title
Biophysical journalauthors
Tian L,Gwizdala M,van Stokkum IH,Koehorst RB,Kirilovsky D,van Amerongen Hdoi
10.1016/j.bpj.2012.03.008subject
Has Abstractpub_date
2012-04-04 00:00:00pages
1692-700issue
7eissn
0006-3495issn
1542-0086pii
S0006-3495(12)00290-1journal_volume
102pub_type
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