Abstract
An R-phycoerythrin (R-PE) was isolated by gel filtrations on Sepharose CL-4B and Sephadex G-150 from the phycobiliprotein extract of the marine red macroalga Polysiphonia urceolata Grev and further purified by ion exchange chromatography on DEAE-Sepharose Fast Flow. The purified R-PE showed three absorption peaks at 498 nm, 538 nm, 566 nm and one fluorescent emission maximum at 577 nm. Although the R-PE showed a single band on the examination by native PAGE, it exhibited two very close bands at pH about 4.7 in native isoelectric focusing (IEF). Polypeptide analysis of the R-PE demonstrated that it contained four chromophore-carrying subunits, α18.2, β20.6, γ31.6 (γ'), γ34.6 (γ), and no colorless polypeptide; its subunit composition was 6α18.2:6β20.6:1 γ31.6:2γ34.6. The α and β subunits were distributed within a acidic pH range from 5.0 to 6.0 in denaturing IEF and the γ subunits were in a basic pH range from 7.6 to 8.1. These results reveal that the prepared R-PE may exist in two hexamers of γ (αβ)3 γ (αβ)3γ' and γ (αβ)3 γ'(αβ)3 γ and that the R-PE participate in the rod domain assembly of P. urceolata phycobilisomes by stacking each of its trimer (αβ)3 face-to-face with the aid of one γ subunit (γ or γ').
Highlights
Phycobiliproteins are a family of light-harvesting pigment-protein complexes found widely in cyanobacteria, red algae and some cryptomonads [1, 2, 3, 4]
The chromatogram (Fig. 1a) exhibited that the R-PEs were successfully separated from large molecular substances in dark red color and small molecular substances in light yellow by the gel filtration on Sepharose CL-4B
By the gel filtration on G-150 (Fig. 1b), the R-PEs in the sample from the CL-4B column were adequately separated from R-PC and AP trimers other than from the remaining large and small molecular substances
Summary
Phycobiliproteins are a family of light-harvesting pigment-protein complexes found widely in cyanobacteria, red algae and some cryptomonads [1, 2, 3, 4]. According to their light absorption properties, phycobiliproteins are classified into three main groups: phycoerythrin (PE; λmax = 565–567 nm), phycocyanin (PC; λmax = 615–620 nm) and allophycocyanin (AP; λmax = 650–652 nm) [1,2]. In cyanobacteria and red algae, these phycobiliproteins assemble to form a supermolecular protein complex, named phycobilisome (PBS), by the aid of related linkers [5,6,7]. As major lightharvesting complexes the PBSs make cyanobacteria and red algae able to grow well under the light environments where green algae are hard to live owing to their exclusively using
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