Photosynthetic Electron Transport Chain of Chlamydomonas reinhardi. IV. Purification and Properties of Plastocyanin

Abstract

The copper protein plastocyanin has been found to be an essential component of the photosynthetic electron transport chain of Chlamydomonas reinhardi. This paper describes a method for its isolation and purification from the wild-type strain. In addition, some of its properties are described and compared with those reported for spinach plastocyanin. The plastocyanin was extracted from acetone powders preparaed from intact cell, and it was purified by ion exchange chromatography on DEAE cellulose and gel filtration of Sephadex G-75. The yield of the purified protein ranged from plastocyanin equivalent to 2.0-2.5 [mu]g atoms Cu/1000 [mu]moles chlorophyll. In general the absorption spectrum of plastocyanin from C. reinhardi resembled that of the plastocyanin from spinach. Some spectral differences were found in the ultraviolet region where, in contrast to spinach plastocyanin, that of C. reinhardi had a greater absorbance (relative to peaks in the visible) and less evidence for phenylalanine fine structure. The normal oxidation-reduction potential of C. reinhardi plastocyanin was found to be + 0.37 volts, the same as reported for spinach plastocyanin. The molecular weight of C. reinhardi plastocyanin has been estimated to be 13,000 [plus or minus] 2000. In contrast, the value for spinach plastocyanin has been found to be 21,000.