Allophycocyanin complexes from the phycobilisome of a thermophilic blue-green alga Myxosarcina concinna Printz

摘要

the core polypeptide components of the intact phycobilixomes (PBSs) prepared by the sucrose gradients in 0.9M phosphate buffer form a thermophilic cyanobacterium Myxosarcina concinna Printz were investigated.Three allophycocyanins,designated AP1,AP2,and AP3,of the PBS cores were successfully prepared byusing the gradient polyacrylamide gel electrophoresis(PAGE) performed in neutral,instead of alkaline,buffer system.The spectral properties of AP2 and AP3 demonstrated that they both had fluorescence emission maxima at 684/685 nm at 77K,which was identical to those of the intact PBSs,and showed the afbsorption of allophycocyanin B(AP-B) subunit.sodium dodecyl sulfate-PAGE revealed that the three biliprotein complexes were all composed of heterogeneous subunits and two more linker polypeptides (Ls),AP1 alpha~22.3alpha~19.5beta~17.4beta~15.7L~13.8L~11.3L~9.5,AP2alpha~22.3alpha~19.5beta~17.4beta~15.7beta~15.1L~11.3L~9.5,and AP3alpha~22.3alpha~9.5beta~17.4beta~15.7beta~15.1beta~15.1L~11.3L~9.5L~8.3.Compared with the characteristics of AP1,beta~15.1,which belonged to the beta subunit group,was theAP-B subunit of AP2 and AP3.Because AP2 wasonly obtained together with the PBS by the aid of 2%(v/v) Triton X-100,but not AP3,it was closely related to anchoring the PBs core on thylakoid membranes though the polypeptide analysis showed that AP2 had no core-membrane linker (L-CM).Aggregates of the three AP bioliporteins were proposed based on teh present reslts,and their functions in the PBS core construction and the energy transfer to PS II and PS I were discussed.