Cylindrical 52.5-nm-long phycobilisomes were observed inAnabaena variabilis, differing from the generally accepted hemidiscoidal morphology. The central part of such a phycobilisome has a network-like fine structure of slightly greater diameter (16 nm) than the connected end parts of stacked-disc structure (12 nm in diameter). On the basis of this morphology, the molecular mass of this phycobilisome was calculated to be 3.27×106, about 60%of which is accounted for by phycocyanin with the rest being due to allophycocyanin. Separately prepared 23Sallophycocyanin particles with a molecular mass of 1.13×106have the dimensions (16×23 nm) and network-like fine structure similar to the central part of phycobilisomes, while an aggregate form of phycocyanin (18S) has a fine structure of stacked discs similar to the connecting end part of phycobilisomes, suggesting that the central part constitutes the core at which these phycobilisomes attach to the thylakoid membran
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