The preparation and some properties of cytochromef

Abstract

Hill & Scarisbrick (1951) obtained from green leaves two new soluble cytochrome components, calledb3andf. The latter appeared to be a constituent of the chloroplast, and its propel have now been in examined further with particular reference to a companson with cytochromec. A method is described for preparing the component from the leaves of parsley (Petroselinum sativum). Spectroscopic examination of acetone powders of elder and parsley leaves showed that the total cytochrome present bore a similar ratio to total chlorophyll in both species, and about one-third of the total could be obtained in solution by the method described. A similar component was observed spectroscopically in acetone powders of four species of algae. In solution at pH 7 ferrocytochromefdoes not combine with oxygen or carbon monoxide. The spectrum resembles that of ferrocytochromec, but the bands are sharper and are moved towards the red. At pH 7⋅4 ferricytochromefhas a parahaematin type of spectrum. Using ferrocyanide-ferricyanide mixtures as rH buffersin vacuo, the characteristic potential (E0') at pH 6 to 7⋅7 and 30° was 0⋅365 V. In the alkaline range a basic dissociation of ferrricytochrome) (pK = 8⋅4) occurs to giveE0'/pH = -0⋅06 V. The component is denatured by heating above 58°C or at pH below 4 or above 11 to give an autoxidizable haemochromogen. The haem of cytochromefis not removed by acid acetone, and evidence is presented that in addition to iron-protein bonds there are stable linkages between protein and the tetrapyrrol ring resembling those of cytochromec. Qualitative solubility observations indicated an isoelectric point at pH 4⋅7 Sedimentation and diffusion measurements gaves20= 6⋅91 x 10-13and D20= 6⋅1 x 10-7cm2/s. ThusMs= 110,000. The possible significance of cytochromefin the oxidation-reductions of the chloroplast reaction is discussed.