Reconstitution of an allophycocyanin trimer complex containing the C-terminal 21-23 kDa domain of the core-membrane linker polypeptide Lcm.

Allophycocyanin (AP) was isolated from extracts of the cyanobacterium Mastigocladus laminosus. A fraction enriched in AP-associated polypeptides with apparent molecular masses of 21-23 kDa in SDS-PAGE, was isolated on a preparative scale and identified as a homologous mixture of C-terminal fragments of the core-membrane linker polypeptide Lcm. The complex (alpha AP beta AP)3.21-23 kDa was reconstituted and characterized by sucrose density gradient ultracentrifugation, absorption, fluorescence emission and circular dichroism spectroscopy. The 21-23 kDa polypeptides were found to induce spectral changes in AP similar to those induced by the small core linker polypeptide Lc8.9. Possible functions of the complex in phycobilisomes are discussed.