A New Leaf Copper Protein ‘Plastocyanin’, a Natural Hill Oxidant

Abstract

THE occurrence in Chlorella ellipsoidea of a new copper protein, able to undergo reversible oxidation-reduction reaction, has been reported by one of us (S. K.)¹. The methods of extraction and purification as well as some properties characterizing the substance have been described. This substance is distinguished from any of the oxidases by the fact that in its reduced form it is unable to react directly with molecular oxygen. Similar substances have since been found to occur in the green leaves of various higher plants (for example, spinach and Chrysanthemum coronarium). In view of its localization in the chloroplasts, and its characteristic blue colour in the oxidized form, the name ‘plastocyanin’ is proposed for this copper protein. Further work has been done to elucidate the behaviour of plastocyanin during photosynthesis. In this communication, the photo-reduction (Hill reaction) of this substance and its effect on the photo-reduction of other known Hill reagents are briefly described.