The 42.1 and 53.7 kDa bands in SDS-PAGE of R-phycoerythrin from Polysiphonia urceolata

In SDS-PAGE gels of three purified R-phycoerythrins (R-PEs) isolated from three species of red algae, two bands whose molecular weights were about 40 kDa and 50 kDa can stably be found when the sample loading amount was enough. It is important for structure study of R-PE to clarify what these bands represent and how they are formed. According to results of the second SDS-PAGE, as well as molecular weights, fluorescences under UV and abundance, the 42.1 kDa and 53.7 kDa bands in SDS-PAGE gels of R-PE from Polysiphonia urceolata were believed to be complexes of αβ and βγ1, respectively. Formation of these bands may be related to light and phycourobilins (PUB) in subunits; and appearance of these two bands provided some proofs on position of chromophores and directions of energy transfer in R-PE. R-PE containing γ1 subunit was obviously more stable than R-PE containing γ2 subunit when they were exposed to protein denaturants, so γ subunits of R-PE may play important roles in structural stability of R-PE aggregates and the main forces that maintain the stability of R-PE may be interactions between γ subunit and β subunits.