Spectroscopic studies of Synechococcus sp PCC 7002 phycobilisome core mutants

Thesis/Dissertation · Thu Apr 01 00:00:00 EST 1993

DOI:https://doi.org/10.2172/10151568· OSTI ID:10151568

Gindt, Yvonne Marie ^[1]

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1. Univ. of California, Berkeley, CA (United States)

The role of the L_cm (I), β¹⁸ (II), and α^AP-B (III) chromoproteins in the phycobilisome (PBS) core was investigated using genetically engineered strains of Synechococcus missing different polypeptides. Intact cells, isolated PBS, and subcore preparations for each mutant were studied to determine the effect of that mutation on energy transfer within the PBS core and to the reaction centers. Three mutants lacked the II and/or III polypeptides, while the I chromophore was altered in others. A lower energy absorbing chromophore, A_max = 695 nm, was substituted for the I chromophore. The deletion of the II and III subunits had no discernible effect on energy transfer from the PBS to PSII. In cells and isolated PBS, the altered I chromophore acts to quench the PBS complex and to redirect the energy which would be transferred to PSII. In the PBS and subcore preparations, deletion of the III subunit did not alter energy transfer within the core. The deletion of the II subunit from the PBS caused a small decrease in the excited state lifetimes of the final emitters indicating more disorder within the core. The I chromophore was found to absorb at 670nm and to emit at 683nm within the intact PBS. The II chromophore emits at 679nm while the III chromophore emits at 682nm. A strong interaction exists between the I chromophore and the II subunit. Upon deletion of the II subunit from the PBS core, the I chromophore emits at a higher energy. The II subunit could act to stabilize the I chromophore-binding pocket, or exciton coupling could be occurring between the two. The role of the III chromophore is still unclear at this time. The III chromophore does contribute to the RT emission of the isolated PBS, but it transfers energy to I at 77 K. One can conclude that the III subunit is adjacent to the trimer containing the I polypeptide.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 10151568
• Report Number(s): LBL-33932; ON: DE93013737
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: Apr 1993
• Country of Publication: United States
• Language: English

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CYANOBACTERIA
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FLUORESCENCE SPECTROSCOPY
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