A procedure for isolation of two iso-plastocyanins from parsley has been described here. Three consecutive Chromatographic steps on DE-52-Whatman cellulose were applied for isolation of two total plastocyanin (PC) fractions, oxidized [PC(II)] and reduced [PC(I)]. By chromatofocusing of PC(II) on Polybuffer exchanger 74 two different plastocyanins, designated as plastocyanin a (PCa) and plastocyanin b (PCb), were obtained. The isoelectric points (pI) of PCa and PCb at 10°C are 4.16 and 4.14, respectively. The complete amino acid sequences of PCa and PCb were determined. The two iso-proteins consist of 97 amino acid residues and differ only at sequence position 53, where Glu in PCa is replaced by Asp in PCb.
