Photochemical Reaction Systems of Photosynthesis in Phytolacca americana

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Abstract
Two ferredoxins were isolated from pokeweed, Phytolacca americana, and purified by ammonium sulfate fractionation (60–100% saturation), Sephadex G-50 and DEAE-cellulose column chromatographies, and preparative polyacrylamide disc gel electrophoresis at pH 9.3. The faster running ferredoxin on the gel electrophoresis was designated as Fd I and the slower one as Fd II of P. americana. The absorption spectra of Fd I and Fd II were very similar to those of Scenedesmus and spinach ferredoxins, respectively, exhibiting absorption maxima at 275 (276 for Fd II), 330, 422, and 465 nm. A422/A275 was 0.70 for Fd I and A422/A276 was 0.48 for Fd II. Amino acid compositions were as follows: Fd I; Lys4, His1, Arg1, Asp13, Thr11, Ser6, Glu13, Pro5, Gly7, Ala9, Cys(5), Val9, Ile4, Leu6, Tyr3, Phe3, 100 residues in total: Fd II; Lys3, His1, Arg1, Trp1, Asp9, Thr11, Ser7, Glu14, Pro5, Gly7, Ala13, Cys(5), Val7, Met1, Ile2, Leu3, Tyr4, Phe2, 99 residues in total. Two non-heme irons and two acid-labile sulfides were detected per molecule for both ferredoxins. Molecular weights as determined by Sephadex G-75 column chromatography were 11,500±500 for both ferredoxins and those calculated from the amino acid compositions were 10,617 and 10,438 for Fd I and Fd II, respectively. ε422 of the oxidized form was found to be 9.85×103 for both ferredoxins. The photochemical activities of both ferredoxins as estimated with washed, broken chloroplasts of spinach were found to be almost identical.

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