title: Isolation of monomeric cytochrome f from Japanese radish and a mechanism of autoreduction.
abstract: Monomeric cytochrome f from Japanese radish (Raphanus sativus L. var acanthiformis Makino) leaves was isolated in a homogeneous state with an A420.5/A277 of 7.6. Radish cytochrome f is a single polypeptide chain with a molecular weight of about 33,000. The midpoint potential is 350 mV. The amino acid analysis indicates the existence of 3 residues of half-cystine. Radish cytochrome f contains one thiol group which reacts with 5,5'-dithiobis(2-nitrobenzoic acid) only after denaturation by sodium dodecyl sulfate. Ferricytochrome f is reduced by the superoxide radical at the rate of 6 X 10(6) M-1 s-1 at pH 7.8. Radish ferricytochrome f is also reduced slowly without an exogenous electron donor. A kinetic study and the effect of the thiol reagent indicate that the autoreduction is an intramolecular reaction and that the thiol group is an electron donor.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D003580:Cytochromes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010944:Plants / Q000201:enzymology*; D013053:Spectrophotometry
chemical_list: D000596:Amino Acids; D003580:Cytochromes