The subunits analysis of R-phycoerythrin from marine red algae by isoelectric focusing

Subunit components of R-phycoerythrins (R-PEs) prepared from five marine macro red algae were analyzed by sodium dodecyl sulfate -polyarylamide gel electrophoresis (SDS-PAGE) and by isoelectric focusing (IEF) in pH gradients range of 3.0 to 9.5, 2.5 to 5.0 and 4.0 to 6.5. Riboflavin was used to catalyze polymerization of IEF gel in acidic pH gradients, and ethanolamine and HEPES were selected as cathode buffers for IEF. The pIs of the R-PE subunits existed between pH 4.9 and 5.7. A larger number of bands could be identified from IEF relative to SDS-PAGE, demonstrating that some subunits of the R-PEs which showed a certain apparent molecular weight have different pIs. This revealed that local net charge differences exist among the subunits of the R-PEs which have even the same molecular weight as well as those with various molecular weights, therefore charge-charge interaction among the subunits of the R-PEs may play an adequate role in R-PE assembly, which is consistent with the fact that the R-PEs are insensitive to surface-active reagents.