The R-phycoerythrin-R-phycocyanin Complex Analysis Of The Phycobilisome From Polysiphonia Urceolata Grev

Red alga is a kind of large benthic algae mainly growing in temperate zone and intertidal zone.Red algae are rich in phycoerythrin,which can effectively use 450?650nm visible light and play an indispensable role in the energy transfer and material cycle of marine ecosystem.In the experiment,the marine Polysiphonia urceolata was used as the research object to prepare R-phycoerythrin-R-phycocyanin complex(R-PE-R-PC).The connection between R-PE and R-PC in the complex was analyzed,and the energy transfer pathway between R-PE and R-PC was studied.Multidimension chromatography and native PAGE(Native-PAGE)were used to prepare R-phycocyanin(R-PC)and Allophycocyanin(AP)whose purity meets the requirements of light absorption coefficient determination.The light absorption coefficients of R-phycoerythrin(R-PE),R-PC and AP obtained by the Lowry method with?-globulin as standard protein were more suitable to measure qualitatively protein complexes with multi-subunit components.Two-variable and three-variable linear equations suitable for the determination of protein content and proportion in low concentration were established by taking the individual characteristic light absorbencies(A_ls)of R-PE,R-PC and AP as variables,and used for the analysis of the composition and relative content of phycobiliproteins.Native-PAGE,SDS-PAGE,urea denatured IEF and2-D SDS-PAGE were used to analyze the subunit composition and structural characteristics of R-PE-R-PC.The composition analysis of the phycobiliproteins in phycobilisomes showed that the ratios of R-PE,R-PC and AP in dissociated and intact phycobilisomes were 7?9:1:1and 11?13:1:3,respectively.This difference in composition originates from the intermolecular interaction of R-PC and AP in the intact phycobilisomes,and was conducive to the efficient one-way transfer of light energy.The subunit composition analysis of phycocyanin showed that both R-PC and R-PC2contained one?and two?subunits,and R-PC has four?subunits with different relative molecular masses and isoelectric points:^19.6?_P⁵._C⁷⁰,^18.2?_P⁵._C⁷⁰,^19.6?_P⁵._C⁶¹,^18.2?_P⁵._C⁶¹.Under different preparation methods and storage conditions,the relative content of these four?subunits will change.In the electrophoresis results of the R-PE larger than hexamer and the R-PE-R-PC prepared by sucrose density gradient centrifugation:the R-PE larger than hexamer contained four?subunit with different molecular masses and p Is,?₁⁷.⁹,?₁⁸.⁰⁹,?₁⁸.²⁸and?₂⁸.⁰⁹,the relative proportion of?₂⁸.⁰⁹should be less than or equal to 1/4 of the total amount of the?subunits,and there is a colorless polypeptide ³⁸L_R.In addition to ³⁸L_R in the R-PE-R-PC,there is also a colorless polypeptide ^44.8L_R.Comprehensive analysis showed that ^44.8L_Rshould be a linker polypeptide connecting two trimers of R-PC,and ³⁸L_R may be a"rod"domain linker participating in the connection of R-PE and R-PC in the R-PE-R-PC,the structural unit forms of the R-PE-R-PC should be:R-PE₆-³⁸L_R-R-PC₆(R-PE₆-³⁸L_R-(R-PC₃-^44.8L_R-R-PC₃))?R-PE₆-R-PE₆-³⁸L_R-R-PC₆.