A M r 95,000 polypeptide in Porphyridium cruentum phycobilisomes and thylakoids: Possible function in linkage of phycobilisomes to thylakoids and in energy transfer

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Abstract
Two pigmented polypeptides with the same MW (95,000) were isolated from the photosynthetic apparatus of P. cruentum by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. A blue polypeptide from phycobilisomes had absorption and fluorescence emission spectra similar to those of allophycocyanin. A green-pigmented polypeptide from photosynthetic membranes (free of phycobilisomes) contained chlorophyll a. Several properties were common to the 95,000 MW polypeptides from both sources: identical MW, identical gel electrophoresis patterns after limited protease digestion and immunological crossreactivity with an IgG fraction directed against the 95,000 MW polypeptide from phycobilisomes. Apparently, a common polypeptide exists in phycobilisomes and thylakoids and it probably anchors the phycobilisome to the thylakoid membrane. The fluorescence emission overlap of the blue and green polypeptides suggests that they are involved in the transfer of energy from phycobilisomes to thylakoids.