Purification of an acidic plastocyanin from MicroBiomis aeruginosa

Abstract

Plastocyanin and cytochrome c-553 are two functionally equivalent electron carriers in the photosynthetic chain of cyanobacteria. Microcystis aeruginosa, a unicellular cyanobacterium which grows well at a high pH (8.6) and which was not known to possess plastocyanin, has been studied for its ability to synthesize plastocyanin in culture media with and without Cu. In the absence of Cu, an acidic cytochrome c-553 alone was isolated. With the inclusion of 2 μM Cu, cytochrome c-553 synthesis was partially suppressed and an acidic plastocyanin was isolated. A newly developed procedure, using high concentrations of ammonium sulfate to fractionate water-soluble proteins on Sephacryl S-200 was successfully used to isolate and concentrate the plastocyanin, thus allowing it to be further purified to homogeneity. This protein has an isoelectric point of 4.8 which is similar to the pI value reported for otheracidic plastocyanins from higher plants and greenalgae. Its N-terminal sequence of the first 15 aminoacids has been determined; 9 of these amino acidsare identical to those in the sequence of the basicplastocyanin from Anabaena variabilis. © 1989 Elsevier Science Publishers B.V. (Biomedical Division) All rights reserved.