Studies on the b-type cytochromes from mung bean seedlings. 2. Some properties of cytochromes b-555 and b-561

Studies on the b-type cytochromes from mung bean seedlings. 2. Some properties of cytochromes b-555 and b-561

1962

REP.MB-1025

Some properties of the purified cytochromes b-555 and b-561 obtained from etiolated mung bean (Phaseolus aureus) seedlings have been determined. By using ferric-ferrous oxalate buffer systems, the oxidation-reduction potentials at pH7 were found to be -0.030 and +0.002 volts, respectively. Both pigments are reduced immediately by hydrosulfite (dithionite), reduced menadione, and cysteine, but only cytochrome b-561 is rapidly reduced by ascorbate. The prosthetic groups of both cytochromes were identified as protoheme on the basis of their spectral c.haracteristics and chromatographic behavior. The protoheme is removed from the protein by trea ment with acid-acetone. In both cases, the original cytochrome could be reconstituted from the apoprotein and chemically pure protoheme. Studies on the intracellular localization of these cytochromes suggest that they were present originally in the s"oluble mung bean fraction and were not removed from the particles. Comparison of these pigments with the known cytochromes suggests that they have not been described' previously. Cytochrome b-555 resembles the pigment generally associated with the microsomal fraction, and cytochrome b-561 is more similar to the mitochondrial cytochrome.

v.237(9):2955-2964, JOURNAL OF BIOLOGICAL CHEMISTRY

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