Characterization of Plastocyanin Isolated From Brazilian Elodea

Plastocyanin obtained from an aquatic higher plant, Brazilianelodea, was characterized by electronic absorption, CD, andEPR spectroscopy. The blue copper center of Brazilian elodeaplastocyanin is electronically and geometrically similar tothat of terrestrial higher-plant (cucumber, spinach, poplar,etc.) and algal plastocyanins as well as that of another aquatichigher-plant (hornwort) plastocyanin. The midpoint redox potentialof the copper in the plastocyanin was estimated to be +364 mVat pH 7.2, which is in the range of midpoint potentials from+347 to +395 mV reported for plastocyanins. The ratio of Phe/Tyrresidue was determined to be 3 by amino acid analysis. Valuesof 2–3.5 have been commonly observed in many higher-plantplastocyanins; a conspicuous exception to this is hornwort plastocyaninwith a Phe/Tyr value of 9. (Received January 16, 1986; Accepted April 18, 1987)