Purification and Some Properties of Scenedesmus Ferredoxin

A simple procedure for purification of ferredoxin from a green alga, Scenedesmus, is described. Crystalline ferredoxin had an absorption spectrum with maxima at 276, 330, 421, and 464 rnp and with minima at 255, 293, 390, and 445 rnp. The ratios of the optical densities at 421 and 330 rnp to that at 276 rnp were 0.651 and 0.883, respectively. The substance was shown to be pure by disc electrophoresis and sedimentation equilibrium methods. Two atoms of iron and 2 moles of labile sulfur were found per mole of ferredoxin. The amino acid composition was Lysl, HisI, Argl, Trpo, ASPI,, Thrlo, Sers, Glu10, Proh, Gly7, Alalo, CYSG, Valb, Metl, Ile,, Leu?, Tyrd, Pheg, (NH&. The aminoand carboxyl-terminal sequences are Ala-ThrTyr-Lys-Val-Thr-Leu-Lys-Thr-Pro and Leu-Phe, respectively. The activity of ferredoxin was assayed by the photoreduction of TPN with illuminated spinach chloroplasts. Ferredoxins of spinach, Swiss chard, and Scenedesmus were found to have identical activities.