At both room temperature (RT) and 77 K, the absorption and fluorescence spectra of the three individual chromophore types (α84, β84, and β155) found in monomeric C-phycocyanin (αPCβPC), isolated from the cyanobacterium Synechococcus sp. PCC 7002, were resolved along with the rates of energy transfer between the chromophores. The cpcB/C155S mutant, whose PC is missing the β155 chromophore, was useful in effecting this resolution. At RT, the single broad peak in the visible region of the absorption spectrum of (αPCβPC) was resolved into its three-component spectra by comparing the steady-state absorption spectra of the isolated wild-type α subunit of PC (αPC) (containing only the α84 chromophore) with those of the monomeric PCs isolated from the mutant strain (αPCβ*) and the wild-type strain (αPCβPC). At 77 K, the visible region of the absorption spectrum of (αPCβPC) splits into two peaks. This partial resolution at 77 K of the chromophore spectra of (αPCβPC) when compared with the 77 K absorption spectra of αPC, βPC, and (αPCβ*) provided a confirmation of our RT assignments of the chromophore absorption spectra. The individual fluorescence spectra of the chromophores and the rate constants for energy transfer between them in (αPCβPC) were resolved by modeling the time-resolved fluorescence spectra of βPC (containing the β155 and β84 chromophores) and (αPCβ*). As with absorption, lowering the temperature to 77 K helped resolve the fluorescence spectra of the individual chromophores because the spectra were narrowed.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry