Isolation and Characterization of PC645 in Binding State from Chroomonas placoidea
A Chl-protein band named Band Ⅲ containing phycocyanin PC645 in binding state is isolated from Chroomonas placoidea by using the method of sucrose density gradient centrifugation.The results of ammonium sul-fate fractionation show that 50％ammonium sulfate precipitation can remove most of the Chl-protein complexes in Band Ⅲ and effectively avoid the loss of PC645.Spectral and peptide analysis demonstrate that the subunit type of the most abundant band Band Ⅰ is β1,indicating that the α1α2β1β1 heterodimer form predominated in PC645 is mainly free in the thylakoid lumen.While,the heterodimer containing 2 subunit enriched in Band Ⅲ is probablyα1α2β1 β2,which exhibits higher hydrophobicity and therefore more susceptible to be salted out.Band Ⅲ after am-monium sulfate fractionation is subject to hydrophobic chromatography.The eluted fraction 1 with relatively lower hydrophobicity contains both PC645 and Chl a-protein.The eluted fraction 4 with relatively highest hydrophobicity is recognized as fully purified PC645 containing almost no chlorophyll,and most likely the PC645 component of Band Ⅲ in binding state to Chl-protein.These results lay a foundation for structure and interaction studies between the two sets of light-harvesting systems in cryptophytic algae in the future.
Chroomonas placoideaPC645-chlorophyll-protein complexsucrose density gradient centrifugationammonium sulfate fractionationhydrophobic chromatography
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